Evaluation of the hazard of light emitted during arc welding
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Title Evaluation of the hazard of light emitted during arc welding
Author(s) 中島, 均
Citation 北海道大学. 博士(環境科学) 乙第7039号
Issue Date 2017-12-25
DOI 10.14943/doctoral.r7039
Doc URL http://hdl.handle.net/2115/68191
Type theses (doctoral)
File Information Hitoshi_Nakashima.pdf
Hokkaido University Collection of Scholarly and Academic Papers : HUSCAP
Evaluation of the hazard of light emitted during arc welding
(アーク溶接時に放射される光の有害性の評価)
Hitoshi NAKASHIMA
i
Table of contents
Evaluation of the hazard of light emitted during arc welding
by Hitoshi NAKASHIMA
Chapter I: Grand Introduction ・・・・・・・・・・・・・・・・・ 1
1.1 Introduction ・・・・・・・・・・・・・・・・・・・・・・・・ 1
1.2 Hazards of light ・・・・・・・・・・・・・・・・・・・・・ 2
1.2.1 Ultraviolet radiation (UVR) ・・・・・・・・・・・・・・ 5
1.2.2 Blue light (Visible radiation) ・・・・・・・・・・・・・ 7
1.3 Hazardous optical radiation emitted by arc welding ・・・・・・・ 10
1.3.1 Outline of arc welding ・・・・・・・・・・・・・・・・ 10
1.3.2 Welding arc ・・・・・・・・・・・・・・・・・・・・ 13
1.3.3 Health disorders caused by welding arc・・・・・・・・・・ 14
1.4 Objective of this research ・・・・・・・・・・・・・・・・・・ 16
1.5 Composition of this thesis ・・・・・・・・・・・・・・・・・・ 19
1.6 References ・・・・・・・・・・・・・・・・・・・・・・・・ 21
Chapter II: Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc
Welding of Aluminum Alloys ・・・・・・・・・・・・・・・・・・・
26
Abstract ・・・・・・・・・・・・・・・・・・・・・・・・・・・ 26
2.1 Introduction ・・・・・・・・・・・・・・・・・・・・・・・ 26
2.2 Methods ・・・・・・・・・・・・・・・・・・・・・・・・・ 29
2.2.1 Impact of the type of base metal, the type of filler rod, and the
magnitude of the welding current ・・・・・・・・・・・・
32
ii
2.2.2 Dependence on the direction of emission from the arc ・・・・ 35
2.2.3 Impact of the type of electrode ・・・・・・・・・・・・・ 36
2.3 Results ・・・・・・・・・・・・・・・・・・・・・・・・・ 37
2.4 Discussion ・・・・・・・・・・・・・・・・・・・・・・・・ 41
2.5 Conclusions ・・・・・・・・・・・・・・・・・・・・・・・ 45
2.6 References ・・・・・・・・・・・・・・・・・・・・・・・・ 45
Chapter III: Study of Ultraviolet Radiation Emitted by Gas Metal Arc
Welding of Aluminum Alloys ・・・・・・・・・・・・・・・・・・・
48
Abstract ・・・・・・・・・・・・・・・・・・・・・・・・・・・ 48
3.1 Introduction ・・・・・・・・・・・・・・・・・・・・・・・ 49
3.2 Hazard assessment of the UVR ・・・・・・・・・・・・・・・・ 50
3.3 Methods ・・・・・・・・・・・・・・・・・・・・・・・・・ 51
3.3.1 Impact of the welding current and the combinations of a base
metal and a welding wire ・・・・・・・・・・・・・・・
53
3.3.2 Dependence on the direction of emission from the arc ・・・・ 56
3.3.3 Influence of the pulsed current ・・・・・・・・・・・・・ 58
3.4 Results ・・・・・・・・・・・・・・・・・・・・・・・・・ 58
3.5 Discussion ・・・・・・・・・・・・・・・・・・・・・・・・ 61
3.5.1 Impact of the magnitude of the welding current and the
combinations of base metal and welding wire ・・・・・・・
63
3.5.2 Dependence on the direction of emission from the arc ・・・・ 64
3.5.3 Influence of pulsed current ・・・・・・・・・・・・・・ 66
3.6 Conclusions ・・・・・・・・・・・・・・・・・・・・・・・ 70
3.7 References ・・・・・・・・・・・・・・・・・・・・・・・・ 70
iii
Chapter IV: Hazard of Ultraviolet Radiation Emitted in Gas Metal Arc
Welding of Mild Steel ・・・・・・・・・・・・・・・・・・・・・
72
Abstract ・・・・・・・・・・・・・・・・・・・・・・・・・・・ 72
4.1 Introduction ・・・・・・・・・・・・・・・・・・・・・・・ 73
4.2 Methods ・・・・・・・・・・・・・・・・・・・・・・・・・ 75
4.2.1 Influence of the type of shielding gas and the magnitude of the
welding current ・・・・・・・・・・・・・・・・・・・
78
4.2.2 Influence of pulsed current ・・・・・・・・・・・・・・ 78
4.3 Results ・・・・・・・・・・・・・・・・・・・・・・・・・ 79
4.4 Discussion ・・・・・・・・・・・・・・・・・・・・・・・・ 81
4.4.1 Influence of the type of shielding gas and the welding current 82
4.4.2 The influence of pulsed current on the UVR hazard・・・・・ 85
4.5 Conclusions ・・・・・・・・・・・・・・・・・・・・・・・ 87
4.6 References ・・・・・・・・・・・・・・・・・・・・・・・・ 87
Chapter V: Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc
Welding and Gas Metal Arc Welding of Magnesium Alloys ・・・・・・・
91
Abstract ・・・・・・・・・・・・・・・・・・・・・・・・・・ 91
5.1 Introduction ・・・・・・・・・・・・・・・・・・・・・・・ 92
5.2 Hazard assessment of UVR ・・・・・・・・・・・・・・・・・ 93
5.3 Methods ・・・・・・・・・・・・・・・・・・・・・・・・・ 94
5.3.1 Outline of experimental welding・・・・・・・・・・・・・ 94
5.3.2 Measured effective irradiance of UVR ・・・・・・・・・・ 95
5.3.3 Influence of the magnitude of welding current ・・・・・・・ 98
5.3.4 Impact of the type of electrode and the shielding gas components 98
5.4 Results ・・・・・・・・・・・・・・・・・・・・・・・・・ 99
iv
5.5 Discussion ・・・・・・・・・・・・・・・・・・・・・・・・ 101
5.5.1 Influence of the magnitude of welding current on hazard of
UVR ・・・・・・・・・・・・・・・・・・・・・・・
102
5.5.2 Influence of the type of electrode and components of the
shielding gas・・・・・・・・・・・・・・・・・・・・・
103
5.6 Conclusions ・・・・・・・・・・・・・・・・・・・・・・・ 107
5.7 References ・・・・・・・・・・・・・・・・・・・・・・・・ 107
Chapter VI: Blue-light Hazard from Gas Metal Arc Welding of Aluminum
Alloys ・・・・・・・・・・・・・・・・・・・・・・・・・・・・・
110
Abstract ・・・・・・・・・・・・・・・・・・・・・・・・・・・ 110
6.1 Introduction ・・・・・・・・・・・・・・・・・・・・・・・ 111
6.2 Methods ・・・・・・・・・・・・・・・・・・・・・・・・・ 113
6.2.1 Influence of the welding current and the use of pulsed current 117
6.2.2 Influence of the type of base metal and the type of welding wire 117
6.3 Results ・・・・・・・・・・・・・・・・・・・・・・・・・ 118
6.4 Discussion ・・・・・・・・・・・・・・・・・・・・・・・・ 122
6.5 Conclusions ・・・・・・・・・・・・・・・・・・・・・・・ 124
6.6 References ・・・・・・・・・・・・・・・・・・・・・・・・ 125
Chapter VII: Summary and conclusions ・・・・・・・・・・・・・・・ 128
7.1 Hazard of UVR ・・・・・・・・・・・・・・・・・・・・・・ 128
7.1.1 Hazard level of UVR in this study ・・・・・・・・・・・ 129
7.1.2 Factors affecting hazard level of UVR ・・・・・・・・・ 130
7.2 Hazard level of blue light in this study ・・・・・・・・・・・・・ 133
7.3 Measures against light emitted during arc welding ・・・・・・・・ 134
7.3.1 Welding workers ・・・・・・・・・・・・・・・・・・ 135
v
7.3.2 Surrounding workers engaged in work other than welding ・・ 136
7.4 Application of the results of this research ・・・・・・・・・・・・・ 137
7.4.1 Adaptation example of quantitative evaluation on UVR shielding
performance for work clothes ・・・・・・・・・・・・・
140
7.4.2 Adaptation example of quantitative evaluation of light shielding
performance against blue light for filter lens and filter plates・・
142
7.5 General conclusion ・・・・・・・・・・・・・・・・・・・・ 144
7.6 References ・・・・・・・・・・・・・・・・・・・・・・・・ 148
Acknowledgments ・・・・・・・・・・・・・・・・・・・・・・・・ 152
vi
Chapter Ⅰ
Grand Introduction
1
Chapter Ⅰ
Grand Introduction
1.1 Introduction
Light is one of the indispensable elements for mankind to live. However, light is also
hazardous, such as playing a central role in the mechanism of the destruction of the ozone
layer and the occurrence mechanism of global warming. In addition, light directly affects
the human body. Ultraviolet radiation (UVR) is the cause of such as keratoconjunctivitis,
dermatitis, cataract and skin cancer, and blue light causes photoretinopathy. Although these
light sources are various, the arc emitted during arc welding is well known as an artificial
light source that generates strong ultraviolet radiation and blue light at the same time.
Arc welding, a fundamental technology of the manufacturing and construction
industries, is widely used in the production of various industrial products, such as vehicles,
large metal structures, electrical products and household products. Thus, arc welding plays
an extremely vital role in many industrial fields. However, many hazards, such as fumes
(powder dust), poisonous gases, spatter (sparks), electrical shocks and hazardous optical
radiation, are emitted during arc welding. These hazardous emissions can affect the health
of workers and cause disastrous occupational accidents. In Japan, there are presumably over
one million people involved in arc welding, with as many as 300,000 professional arc
welders and an additional number of people who perform arc welding as part of their work.
Furthermore, at workplaces where arc welding is performed, workers engaged in tasks other
than welding may suffer health effects from the hazardous emissions from the arc welding.
In these circumstances, measures to protect workers from the health disorders due to
fumes, poisonous gases and electrical shock from arc welding have been enforced by the
Ordinance on Prevention of Hazards due to Dust and the Ordinance on Industrial Safety and
Health, both of which have been enacted by the Japanese government. On the other hand,
Chapter Ⅰ
Grand Introduction
2
health disorders due to spatter have been countered by measures that compel welders to
wear personal eye protectors1), personal face protectors for welding2), protective leather
gloves for welders3) and protective footwear4) specified by the Japanese Standards
Association (JIS). These countermeasures have reduced the number of incidences of health
disorders and disastrous occupational accidents caused by fumes, poisonous gases, electrical
shock and spatter. JIS has enacted standards for protectors that shield light5) and personal
face protectors for welding as measures against the health disorders caused by hazardous
optical radiation, and the Department of Labor (presently the Ministry of Health, Labor and
Welfare) issued a notification on the usage of protectors for shielding light (Notification No.
773: Usage of Protectors for Light Shield) in 1981. Nevertheless, at welding sites, there are
still numerous incidences of eye injuries. Thus, it is safe to say that the effect of current
countermeasures against hazardous optical radiation is limited and insufficient.
1.2 Hazards of light
Light is an essential element of human life, but it can be also hazardous. In fact, there are a
number of light sources at manufacturing sites that can be injurious. However, the hazards
of light are not well known, even by safety and health experts. For any risks associated with
hazardous optical radiation, it is desirable to have correspondingly appropriate assessments
of the hazards.
Electromagnetic waves having a wavelength ranging from 1 nm to 1 mm are defined
as “light”6). This light is roughly classified according to the wavelength as UVR, visible
radiation or infrared radiation. Although UVR and infrared radiation are invisible, they
exhibit physical properties that are similar to those of visible radiation. Moreover, because
these three different types of radiation often occur concurrently, they are collectively called
“optical radiation.” In cases where the intensity of this radiation can be injurious, it is called
Chapter Ⅰ
Grand Introduction
3
“hazardous optical radiation.” Table 1.1 shows seven optical categories of radiation
classified by the International Commission on Illumination (CIE)7) and the main adverse
effects of each category on biological tissue.
Table 1.1 Seven spectral bands of the optical spectrum classified by CIE, where the most
crucial adverse effects on biological tissue are limited to two or three spectral bands
Type of optical
radiation CIE band Adverse effect
UVR
UV-C
100–280 nm
Keratoconjunctivitis, erythema,
skin cancer
UV-B
280–315 nm
Keratoconjunctivitis, erythema,
skin cancer, cataracts
UV-A
315–400 nm
Skin cancer, cataracts,
thermal skin burns
Visible radiation
Visible radiation
about (400–780 nm)
Retinal burns,
thermal skin burns
Blue light
about (400–500 nm) Retinal injuries
Infrared radiation
IR-A
780–1,400 nm
Corneal burns, retinal burns,
thermal skin burns
IR-B
1,400–3,000 nm
Corneal burns, cataracts,
thermal skin burns
IR-C
3,000–1 mm
Corneal burns, cataracts,
thermal skin burns
Generally, the hazards of light are evaluated in accordance with the recommendations
of the American Conference of Governmental Industrial Hygienists (ACGIH)8). In this case,
the term equivalent to “permissible amount” is “threshold limit value (TLV).” In this study,
the TLVs is a time weighted average. The weighted average exposure time is an 8-hour
workday and 40-hour workweek. Most workers are free from any adverse effects on their
health, even if they are repetitively exposed to such working conditions.
Chapter Ⅰ
Grand Introduction
4
Incidentally, the hazards from infrared radiation are generally very weak, so it is
assumed that they will not cause any health disorders. In view of this, this study excludes
infrared radiation, and focuses on UVR and visible radiation (blue light).
The action of optical radiation on biological tissue can be classified into two
categories: photochemical action and thermal action. The photochemical action specifically
means that a molecule in a biological body absorbs a particle (photon) of optical radiation,
is excited, and initiates a chemical action. One of the characteristics of the photochemical
action is its high accumulativeness. In particular, UVR can caused direct and indirect (free
radicals such as reactive oxygen species) DNA damage. Although a living body has a
recovery mechanism against DNA damage, there is a limit to the repair rate of DNA.
Damage to DNA beyond the limits accumulates and causes aging and canceration. Due to
this characteristic, therefore, even if the level of optical radiation is low, and health disorders
could be caused by long-term exposure to the photochemical action. On the other hand, the
thermal action specifically means that the temperature increases when the biological tissue
absorbs the energy from the optical radiation. Because the heat generated by the absorption
of optical radiation energy within the tissue diffuses circumferentially and momentarily, the
accumulativeness of the thermal action is low. Therefore, unlike health disorders caused by
photochemical action, those due to thermal action are caused by being exposed to optical
radiation at a certain intensity. Generally, in photochemical action, optical radiation with a
short wavelength is intense, and each photon has a large energy. On the other hand, thermal
action does not depend on the wavelength of the light. For this reason, health disorders due
to the photochemical action of UVR and blue light are a concern.
The adverse effects of UVR and blue light on the human body differ. As shown in
Figure 1.1, as to the adverse effects on human eyes, for example, because UVR is mostly
absorbed into the surface of the eyes (1% or less of UVR reaches the retina), UVR primarily
Chapter Ⅰ
Grand Introduction
5
damages the cornea and conjunctiva. In contrast, blue light is transmitted through the lens,
and adversely affects the retina. This study provides insight into the hazards of UVR and
blue light.
Figure 1.1. Areas of the human eye adversely affected by UVR (purple arrows) and blue
light (blue arrow)
1.2.1 Ultraviolet radiation (UVR)
Light with a wavelength of approximately 400 nm, which is the lower limit of visible light,
appears purple to human eyes. Based on this, the radiation shorter in wavelength than visible
light but longer in wavelength than approximately 1 nm is called UVR. UVR having a
wavelength of 190 nm or shorter is called “vacuum ultraviolet,” is strongly absorbed by
oxygen molecules, and consequently is not transmitted through the air. Accordingly, people
are not exposed to this type of UVR except in very special cases, a low-pressure mercury
lamp, a xenon lamp and excimer lasers etc., which makes it unnecessary to consider the
exposure to such UVR under normal conditions.
The depth that UVR reaches when entering the human body depends on its wavelength,
with longer wavelengths passing deeper into the body. In the case of the eyes, for example,
Cornea
Conjunctiva
Lens Blue light UVR
UVR
Retina
Chapter Ⅰ
Grand Introduction
6
UVR with a wavelength of 280 nm or shorter, is mostly absorbed by the cornea, and does
not reach deeper areas of the eye. However, UVR with a wavelength of 300 nm or longer is
partly transmitted through the cornea to the lens, where it is absorbed.
UVR strongly affects biological tissue, and, for this reason, causes various health
disorders9-13). Moreover, UVR is strongly absorbed by proteins and water. Consequently, if
UVR enters biological tissue, it is mostly absorbed into the surface of the tissue. This limits
the health disorders due to UVR to surface tissue. Acute health effects from exposure to
UVR include keratoconjunctivitis and erythema, and delayed health effects include cataracts
and skin cancer. As the symptoms of acute health effects, keratoconjunctivitis is
accompanied by photophobia (light sensitivity.), nociception (pain), epiphora (excessive
watering of the eye), decreased visual acuity, foreign-body sensation (gritty sensation),
conjunctiva, etc. If the symptoms are severe, opening the eyes may be difficult. These
symptoms appear in a few hours after exposure to UVR, but resolve in a single day or so.
In the case of erythema (redness), blistering and other symptoms appear a few hours after
exposure to UVR, but resolve in a few days or so. However, if the symptoms are severe, the
skin exfoliates after a few days.
The major sources of health-damaging UVR include the sun9,12), arc welding10,11),
plasma cutting arc, low-pressure mercury lamps (e.g., sterilization lamps)13), and high-
pressure discharge lamps used as industrial ultraviolet lamps.
The hazard level of the acute health effects (e.g., keratoconjunctivitis and erythema)
caused by UVR can be expressed by the effective irradiance (Eeff, mW/cm2) calculated using
Equation (1) under the evaluation standards of ACGIH:
Eeff = ∑ Eλ ·
400
180
S(λ) · ∆λ, ・・・・・(1)
Chapter Ⅰ
Grand Introduction
7
where Eλ is the spectral irradiance mW/(cm2·nm) of the wavelength λ, and S(λ) is the
relative spectral effectiveness at wavelength λ (Figure 1.2). Δλ is the bandwidth (nm).
The TLV at 270 nm, which is the integral of the effective irradiance for 8 h per day, is
3 mJ/cm2. Therefore, the maximum exposure time: tmax (s) per day against the effective
irradiance when the unprotected skin or eye is irradiated with UVR is obtained using
Equation (2):
tmax =3
Eeff. ・・・・・(2)
Figure 1.2. Relative spectral effectiveness showing hazard level according to light
wavelength
1.2.2 Blue light (Visible radiation)
Because the response of photoreceptors in the eye to visible radiation is not precisely the
same between individuals, the wavelength range of visible radiation has not yet been
precisely defined. Generally, however, the lower limit of the wavelength range is from 360
to 400 nm and the upper limit is from 760 to 830 nm6). Of all the visible radiation, the short-
wavelength components (from approximately. 400 nm to approximately. 500 nm) appear
Chapter Ⅰ
Grand Introduction
8
blue to humans. Thus, the visible radiation having such short wavelengths is generally
referred to as blue light.
Of all the parts of the eye, the retina is the most susceptible to the effects of visible
radiation. The internal structure of the eyeball from the cornea to the retina is transparent to
visible radiation. The visible radiation enters the eyeball and reaches the retina with little
attenuation. As shown in Figure 1.3, visible radiation converges at a specific portion of the
retina due to refraction as it passes through the cornea and lens. This area of convergence is
the most likely place for retinal damage to occur.
Figure 1.3. Schematic diagram of the absorption of visible radiation into the eye
Among visible radiation, blue light causes photochemical retinal disorders due to
photochemical action. These disorders are observed as a change in the retina, such as edema
or a hole, and are accompanied by symptoms, such as decreased visual acuity, blurred or
foggy vision and scotoma (a blind spot or area of the visual field with reduced sensitivity).
These symptoms appear immediately or within a single day after exposure, and then
gradually resolve, but can remain for a few weeks to a few months, and, in some cases,
become permanent. The retinal disorders can be severe enough to adversely affect activities
Light source
Eye
Chapter Ⅰ
Grand Introduction
9
of daily living (ADL).
The major sources of health-damaging blue light are the sun and welding arcs. The
hazard of a retinal disorder due to blue light is expressed by the effective blue-light radiance
(LB, W/cm2·sr) of the light source, which is defined by Equation (3):
LB = ∑ Lλ ·
700
305
B(λ) · ∆λ, ・・・・・(3)
where Lλ is the spectral radiance W/(cm2·sr·nm) of the wavelength λ, and B(λ) is the blue-
light hazard function; that is, the function of the hazard level according to the wavelength,
which is stipulated by ACGIH. Figure 1.4 shows the blue-light hazard function, where Δλ
is the bandwidth (nm).
According to the guidelines set forth by ACGIH regarding the hazards of blue light, if
the exposure time to blue light per day is shorter than 104 s (approximately 2.8 h) per a day,
the value of the integral of the effective blue-light radiance should not exceed 100 J/cm2·sr.
Therefore, when the effective radiance of blue light is constant over time, the maximum
acceptable exposure duration in one day, tmax (s), based on the effective blue-light radiance
can be obtained using Equation (4):
tmax =100
LB. ・・・・・(4)
ACGIH has also stipulated that, when the exposure time per day exceeds 104 s, the
effective blue-light radiance should not exceed 0.01 W/cm2·sr.
Chapter Ⅰ
Grand Introduction
10
Figure 1.4. Blue-light hazard function showing hazard level according to light
wavelength
1.3 Hazardous optical radiation emitted by arc welding
The most important source of optical radiation from industrial applications is the welding
arc of arc welding. Arc welding is notorious for generating intense hazardous optical
radiation. Because the welding arc is emitted into the surrounding environment in the
absence of a barrier, it is presumed that many workers are exposed to the hazardous optical
radiation in places where arc welding is performed. In Japan, there are at least 300,000
professional arc welders. There are also the workers who assist the professional welders,
those who perform arc welding as part of their work and those who engaged in work other
than arc welding around the arc welding operation. In total, over one million people are
engaged in arc welding. Many of them are presumed to work in environments that put them
at risk for exposure to welding arcs.
1.3.1 Outline of arc welding
Arc welding is one of typical means used for joining metallic materials. A continuous arc is
generated between a base metal (the metal to be welded) and an electrode, and the base
Chapter Ⅰ
Grand Introduction
11
metal and a filler metal (the metal to be added during the welding) are molten and mixed by
the heat generated by arc. Arc welding, a fundamental technology of the manufacturing and
construction industries, is widely used in the production of various industrial products, such
as vehicles, large metal structures, electrical products and household products.
The arc is a type of discharge phenomenon within a gas, and it emits an intense light
at a high temperature. Arcs visible in daily life include the sparks emitted from pantographs
of Shinkansen bullet trains and those from a live outlet when an electrical cord is removed.
The center temperature of the arc generated during arc welding depends on the welding
method and conditions, but can be more than 13000 K14). This extreme temperature, which
is far above the boiling points of steel and aluminum, partially vaporizes the metal.
The metal, which is heated by the arc and directly exposed to the atmosphere, degrades
in quality due to oxidation, nitriding, etc. Various arc welding methods have been developed
to prevent this degradation in quality. One method performs with blowing shielding gas
around the portion being welding to protect and cool the melted metals. This method is
known as gas-shielded metal arc welding and use a different shielding gas which include
argon (Ar) gas, helium gas, carbon dioxide (CO2) gas, and Ar-CO2 mixed gas. Gas shielded
metal arc welding produces a high-quality weld and is easily adaptive to automatization.
Thus, it is frequently applied in manufacturing. In gas shielded metal arc welding, gas metal
arc welding (GMAW) and gas tungsten arc welding (GTAW) are commonly applied. In
view of this, this research investigates the arc generated during GMAW and GTAW.
GMAW is an arc welding process using an arc between a continuous filler metal
electrode (welding wire) and a molten pool and is a semi-automatic welding process in
which the welding wire is automatically supplied to the portion being welded. Further,
GMAW has high working efficiency, it is currently the most used welding process to be
performed. Figure 1.5 shows the state of GMAW operation.
Chapter Ⅰ
Grand Introduction
12
GTAW is an arc welding process using an arc between a tungsten electrode (non-
consumable) and a molten pool. In this method, a welding operator holds a welding torch
with one hand and holds a filler rod with the other hand to perform the welding operation.
welds, GTAW is used for high-quality welding and welding of thin plates. Figure 1.6 shows
the state of GTAW operation.
Figure 1.5. Work scenery of GMAW. A welding wire is automatically supplied during the
arc.
Figure 1.6. Work scenery of GTAW. A filler rod is inserted into a molten pool which is a
localization liquid pool of molten metal in prior to its solidification as weld metal, and an
inert gas is used as the shielding gas.
Arc
Electrode
Filler rod
Arc
Welding wire
Chapter Ⅰ
Grand Introduction
13
1.3.2 Welding arc
Figure 1.7 shows the wavelength distributions of the arc generated during GMAW of mild
steel. As shown in this figure, the arcs generated during arc welding concurrently emit light
in three wavelength regions of UVR, visible radiation and infrared radiation to the
surrounding environment. Among them is the UV-C wavelength region, which does not
exist in the natural environment. Figures 1.8 and 1.9 exemplify the distributions of arcs
generated during GMAW of aluminum alloys and magnesium alloys, respectively. The arc
generated during arc welding substantially differs according to the welding material. In
general, in the case of GMAW of aluminum alloys and magnesium alloys, UVR and blue
light account for higher percentages, respectively, compared with GMAW of mild steel.
Moreover, the strength and wavelength distributions vary according to the conditions, such
as welding method, shielding gas, welding current, welding voltage and arc length15-23).
Figure 1.7 Spectral irradiance of arcs in GMAW of mild steel
Chapter Ⅰ
Grand Introduction
14
Figure 1.8 Spectral irradiance of arcs in GMAW of aluminum alloys
Figure 1.9 Spectral irradiance of arcs in GMAW of magnesium alloys
1.3.3 Health disorders caused by welding arc
Among the acute health effects of UVR during arc welding, the most common are
keratoconjunctivitis and erythema. Although the number of incidences of kerato-
conjunctivitis in the surrounding environment of an actual welding operation is presumably
Chapter Ⅰ
Grand Introduction
15
very large, there is a paucity of relevant literature on the topic. According to an investigation
by Emmett et al.11), as many as 92% of all welders have experienced keratoconjunctivitis,
and 40% of them have been affected by erythema on the neck.
According to a questionnaire investigation by the Japan Welding Engineering Society
10), welders complain of the following eye-disorder symptoms due to the arc generated by
arc welding: foreign-body sensation (gritty sensation), eye pain, epiphora and photophobia.
These subjective symptoms have different incubation periods. Welders are exposed to the
arc during arc welding, but the symptoms appear after the welding work and overnight.
However, the symptoms are transient, and normally disappear by the time the workers wake
up the next morning. These transient subjective symptoms suggest that the disorder is
keratoconjunctivitis due to UVR. As many as 86% of all welders have experienced such an
eye disorder. Approximately 45% of the welders who have experienced such an eye disorder
have experienced the same disorder once or more per month (as of the time when the
investigation was made). Most welders (88%) use protectors for shielding light, these
shading numbers and transmittance are shown in Table 1.2, and yet, many of them have
experienced such an eye disorder. Therefore, it is considered that the causes for this include
(a) cases in which workers fail to put on their face shields before striking the arc, ensuring
exposure to UVR; and (b) cases in which workers are exposed to UVR by other workers
performing arc welding at the same workplace.
There are reported cases of retinal damage caused by blue light emitted during arc
welding. These cases involve workers who stared at the arc without wearing appropriate
protective gear24-32). Blue light damages the eyes, which can adversely affect ADL. This
damage is observed as a change in the retina, such as edema or a hole, and is accompanied
by symptoms including decreased visual acuity, blurred vision and scotoma. These
symptoms appear immediately or within a day after exposure, and then gradually resolve
Chapter Ⅰ
Grand Introduction
16
over several weeks to several months. There are cases of complete recovery, but there are
many cases where scotoma and decreased visual acuity become permanent.
Table 1.2 Light shielding ability value of filter (%)
Shading
number
UVR transmittance (MAX) Visible light transmittance
313 nm 365 nm Max Standard Min
8 0.0003 0.013 0.16 0.100 0.061
9 0.0003 0.0045 0.061 0.037 0.023
10 0.0003 0.0016 0.023 0.0139 0.0085
11 0.0003 0.0006 0.0085 0.0052 0.0032
12 0.0002 0.0002 0.0032 0.0019 0.0012
1.4 Objective of this research
Hazardous emissions from arc welding have various adverse effects on welders and those
working around the welding site. Various measures have been taken to counter this problem,
but the countermeasures against welding arc are insufficient. From the perspective of
improving the workplace environment for arc welding operations and the industrial health
of workers, preventive measures against exposure to arcs emitted during arc welding are
desired.
In particular, disorders of the eyes are serious and adversely affect ADL. Establishing
effective preventive measures against eye disorders due to welding arc requires quantitative
evaluation of welding arcs. Arc welding is performed using various materials by applying
different welding methods and conditions, and there may be varying degrees of hazard level
according to the respective welding arc that is emitted. For this reason, it is necessary to
research the hazards of arcs emitted during arc welding under various conditions that mimic
actual welding operations.
For UVR, previous studies have measured the UVR emitted during arc welding
processes, such as mild steel and aluminum alloys, and assessed their acute health effects
Chapter Ⅰ
Grand Introduction
17
by ACGIH guideline18-22, 33-35). In these studies, the effective irradiance of UVR emitted
during gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW) of aluminum
alloys and GMAW of mild steel was measured. Dependence of effective irradiance on the
welding current and adaptation of the inverse square law of distance were also verified. In
arc welding, welding results, such as the shape of weld bead and the depth of fusion, have
been dependent on welding materials (components of a base metal and a filler metal), the
pulsed current, the shielding gas, and the type of electrodes. It is considered that these
elements also have an effect on UVR, because there is a close relationship between the state
of the arc and the welding result. However, the influence of these elements on the hazard
from UVR has not yet been investigated. In addition, because the UVR emitted during arc
welding is influenced by reflections from the surface of a base metal and the liquid surface
of molten pool, and by absorption/scattering due to fumes, the effective irradiance of UVR
is thought to be subjected to the angular dependence. However, it is considered to be
insufficient because the angular dependency of the effective irradiance had only been
investigated regarding the angle from the surface of the base material in GMAW of mild
steel33).
For blue light, a few studies have measured the blue light in arc welding of aluminum
alloys 35-37), one of these has actually measured the effective radiance of blue light emitted
during arc welding of mild steel37). And two studies have determined the effective blue-light
radiance of mild steel and aluminum alloy35,36). In these studies, the effective blue-light
irradiance (spectral irradiance weighted against the blue-light hazard function) was
measured at a fixed distance from the arc. The effective blue-light radiance was then
calculated from the effective blue-light irradiance by using the estimated size (area) of the
arc. However, this method provided inaccurate results, because the arc has no definite
Chapter Ⅰ
Grand Introduction
18
boundaries and consequently no definite size. Thus, no reliable data on the effective blue-
light radiance for arc welding of aluminum alloys are available.
The author provides technical guidance on arc welding of mild steel, stainless steel
and aluminum alloys at the Polytechnic University of Japan. Among them, people who
suffer from keratconjunctivities or dermatitis often appear. In particular, at the time of
GMAW of aluminum alloys, the occurrence frequency of keratconjunctivities and dermatitis
is high, and the symptom is serious. Actually, in the ophthalmologic examination,
abnormalities were found in the skin of the keratoconjunctiva and eyelid for workers tasked
to GMAW of aluminum alloy10). Therefore, the hazard of UVR emitted during GTAW and
GMAW, which is a typical arc welding methods of aluminum alloys, were quantitatively
evaluated. Next, in order to compare with the hazard of UVR emitted during arc welding of
aluminum alloys, the hazardous of UVR emitted in GMAW of mild steel most frequently
carried out in the country was quantitatively evaluated. Furthermore, since the hazard of
UVR emitted during the arc welding of aluminum alloys were strongly influenced by
magnesium contained in the aluminum alloy, the hazardous of UVR emitted during GTAW
and GMAW of magnesium alloy were quantitative evaluated. In addition, the hazard of blue
light emitted during GMAW of aluminum alloys were also quantitatively evaluated, because
the arcs emitted by arc welding of aluminum alloys appeared strong emission in the
wavelength range of blue light. The features of the three types of metallic materials used in
this study are shown below.
Aluminum alloys exhibit excellent properties—light weight, high strength-to-weight
ratio, corrosion resistance, workability, and good appearance—and are widely used as raw
materials for structural products and components in a wide variety of fields, including
manufacture of railway vehicles, automobiles, ships, aerospace instruments, and chemical
instruments. Arc welding is used extensively in portions of the production processes for
Chapter Ⅰ
Grand Introduction
19
these aluminum products. The two primary welding methods for aluminum alloys are
GMAW and GTAW. GMAW is primarily used for base metals of thickness 3 mm or greater,
while GTAW is used for beams of lesser thickness.
Mild steel is the most welded metal material so far. Among them, GMAW of mild steel
is the most widely practiced and applied to various industrial products and building
structures. Currently, mild steel is being converted to aluminum alloy and the like for the
purpose of reducing environmental burden, but it is expected to be widely used in the future
because of high cost and weldability.
Magnesium alloys are promising as structural materials because of their excellent
specific strength and vibration damping properties. However, their flammability and
difficulty in plastic forming have limited the application of these alloys. In recent years,
flame-retardant magnesium alloys and their plastic working technology have been
developed and are expected to be applied to structures in various fields such as railway
vehicles. Moreover, with the development of production technique a welding wire made of
flame-retardant magnesium alloy, welding of magnesium alloys is expected in the future.
The purpose of this thesis is to evaluate the hazard of light emitted to the surrounding
environment during welding operation, the hazard level in relation to the acute health effects
of UVR and blue light emitted during arc welding under suitable various conditions for
actual welding operations quantitatively have been evaluated according to ACGIH
recommendations. Among them, the hazard of UVR and blue light were examined for
welding materials, welding methods and welding conditions, detailed corresponding to the
latest welding technology. Experimental methods with high reliability and reproducibility
were adopted for the investigation.
1.5 Composition of this thesis
Chapter Ⅰ
Grand Introduction
20
This thesis is organized based on the background and a series of considerations as stated in
the above. Chapters 2–5 describe the research into the hazards of UVR during arc welding,
and Chapter 6 describes the research into the hazards of blue light during arc welding. Table
1.3 summarizes the relationships between the evaluation of hazardous optical radiation
discussed in this thesis and the welding materials.
Table 1.3 Evaluation of hazardous optical radiation and welding materials
Aluminum alloys Mild steel Magnesium alloys
UVR Chapters 2 and 3 Chapter 4 Chapter 5
Blue light Chapter 6 - -
The content of each Chapter is summarized as follows:
Chapter II
In this chapter, I evaluated quantitatively the hazard of UVR emitted during GTAW of
aluminum alloys. In particular, I studied the impact of (i) the type of base metal, the type of
filler rod, and the magnitude of the welding current, (ii) the direction in which UVR is
emitted from the arc, and (iii) the type of electrode.
Chapter III
In this chapter, I evaluated quantitatively the hazard of UVR emitted during GMAW of
aluminum alloys. In particular, I studied the impact of (i) the type of base metal, the type of
welding wire, and the magnitude of the welding current, (ii) the direction in which UVR is
emitted from the arc, and (iii) the use of pulsed welding current.
Chapter Ⅰ
Grand Introduction
21
Chapter IV
In this chapter, I evaluated quantitatively the hazard of UVR emitted during GMAW of mild
steel. In particular, we studied the influence of (i) the type of shielding gas and the
magnitude of the welding current, and (ii) using pulsed vs. steady welding current.
Chapter V
In this chapter, I evaluated quantitatively the hazard of UVR emitted during GTAW and
GMAW of magnesium alloys. In particular, I studied the influence of (i) the magnitude of
the welding current, (ii) the type of electrode and the type of shielding gas, and (iii) the type
of welding methods.
Chapter VI
In this chapter, I evaluated quantitatively the hazard of blue light emitted in the GMAW of
aluminum alloys. In particular, we studied the impact of (i) the magnitude of welding current,
(ii) the use of pulsed welding current, (iii) the type of base metal and welding wire.
1.6 References
1) Japan Standards Association, Japan Safety Appliances Association, 2003. Personal eye
protectors, JIS T8147, Japan Standards Association.
2) Japan Standards Association, Japan Safety Appliances Association, 2003. Personal face
protectors for welding, JIS T8142, Japan Standards Association.
3) Japan Safety Appliances Association, 1976. Protective leather gloves for welders, JIS
T8113, Japan Standards Association.
4) Japan Standards Association, Japan Safety Appliances Association, 2006. Protective
footwear, JIS T8101, Japan Safety Appliances Association.
Chapter Ⅰ
Grand Introduction
22
5) Japan Standards Association, Japan Safety Appliances Association, 2003. Personal eye
protectors for optical radiations, JIS T8141, Japan Safety Appliances Association.
6) Japan Standards Association, The Japan Society for Analytical Chemistry, 2007.
Technical terms for analytical chemistry: optical part, JIS K0212, Japan Safety
Appliances Association.
7) International Commission on Illumination, 2011. International lighting vocabulary, CIE
Standard CIE S 017/E: 2011, Vienna, International Commission on Illumination.
8) The American Conference of Governmental Industrial Hygienists, 2015. 2015
Threshold limit values for chemical substances and physical agents and biological
exposures indices, Cincinnati, American Conference of Governmental Industrial
Hygienists.
9) World Health Organization Office of Global and Integrated Environmental Health, 1995.
Health and environmental effects of ultraviolet radiation: a summary of Environmental
health criteria 160: ultraviolet radiation, Geneva, World Health Organization.
10) The Japan Welding Engineering Society, 1980. Shakouhogogu no seinouhyouka tou ni
kansuru chousa kenkyu seika houkokusyo, A research report on the performance of eye
protectors against optical radiation, Tokyo, The Japan Welding Engineering Society. (in
Japanese)
11) Emmet EA, Buncher CR, Suskind RB, Rowe KW, 1981. Skin and eye diseases among
arc welders and those exposed to welding operations, Journal of Occupational Medicine
23: 85–90.
12) Sliney DH, Wolbarsht M, 1980. Safety with Lasers and Other Optical Sources, New
York, Plenum press.
Chapter Ⅰ
Grand Introduction
23
13) Kido M, Kawasaki R, Hosokawa C, Gyhotoku T, Imayama S, 2004. Ultrastructural
study of skin damaged by accidental ultraviolet-c irradiation, The Japanese Journal of
Dermatology 114(12): 1911-1916.
14) Zielińska S, Musioł K, Dzierżęga K, Pellerin S, Valensi F, Izara Ch de, Brand F, 2007.
Investigation of GMAW plasma by optical emission spectroscopy, Plasma Sources
Science and Technology 16(4): 832-838.
15) Ferry JJ, 1954. Ultraviolet emission during inert-arc welding, American Industrial
Hygiene Association Quarterly 15(1): 73-77.
16) Emmett EA, Hortsman SW, 1976. Factors influencing the output of ultraviolet radiation
during welding, Journal of Occupational Medicine 18(1): 41-44.
17) Ingram JW, Hortsman SW, 1977. A filed study of near ultraviolet welding irradiance,
The American Industrial Hygiene Association Journal 38(9): 456-461.
18) Lyon TL, Marshall WJ, Sliney DH, Krial NP, Del Valle PF, 1976. Nonionizing radiation
protection special study No. 25-42-0053-77, Evaluation of the potential from actinic
ultraviolet radiation generated by electric welding and cutting arcs, Maryland, US Army
Environmental Hygiene Agency Aberdeen Proving Ground.
19) Okuno T, 1985. Spectra of optional radiation from welding arcs, Industrial Health 23(1):
53-70.
20) Okuno T, 1986. Measurement of blue-light effective radiance of welding arcs. Industrial
Health 24(4): 213-226.
21) Okuno T, 1987. Measurement of ultraviolet radiation from welding arcs, Industrial
Health 25(3): 147-156.
22) Okuno T, Kohyama N, Serita F, 2005. Ultraviolet radiation from MIG welding of
aluminum, Safety & Health Digest 51(9): 2-5. (in Japanese)
Chapter Ⅰ
Grand Introduction
24
23) Bartley DL, McKinney WN, Wiegand KR, 2010. Ultraviolet emissions from the arc-
welding of aluminum-magnesium alloys, American Industrial Hygiene Association
Journal 42: 23-31.
24) Würdemann HV, 1936. The formation of a hole in the macula: Light burn from exposure
to electric welding, American Journal of Ophthalmology 19(6): 457–460.
25) Naidoff MA, Slinkey DH, 1974. Retinal injury from a welding arc, American Journal of
Ophthalmology 77(5): 663-668.
26) Romanchuk KG, Pollak V, Schneider RJ, 1978. Retinal burn from a welding arc,
Canadian Journal of Ophthalmology13: 120–122.
27) Uniat L, Olk RJ, Hanish SJ, 1986. Welding arc maculopathy, American journal of
ophthalmology 102: 394–395.
28) Cellini M, Profazio V, Fantaguzzi P, Barbaresi E, Longanesi L, Caramazza R, 1987.
Photic maculopathy by arc welding, A case report, International Ophthalmology 10:
157–159.
29) Brittain GPH, 1988. Retinal burns caused by exposure to MIG-welding arcs of two cases,
British journal of ophthalmology 72(8): 570-575.
30) Power WJ, Travers SP, Mooney DJ, 1991. Welding arc maculopathy and fluphenazine,
British journal of ophthalmology 75(7): 433–435.
31) Fich M, Dahl H, Fledelius H, Tinning S, 1993. Maculopathy caused by welding arcs, A
report of 3 cases, Acta ophthalmologica 71(3): 402-404.
32) Arend O, Aral H, Reim M, Wenzel M, 1996. Welders maculopathy despite using
protective lenses, Journal of Retinal and Vitreous Diseases 16(3): 257–259.
33) Okuno T, Ojima J, Saito, H, 2001. Ultraviolet radiation emitted by CO2 arc welding, The
Annals of Occupational Hygiene 45(7): 597–601.
Chapter Ⅰ
Grand Introduction
25
34) Okuno T, Saito H, Hojo M, Kohyama N, 2005. Hazard evaluation of ultraviolet radiation
emitted by arc welding and other processes, Occupational Health Journal 28(6): 65-71.
(in Japanese)
35) Peng C, Lan C, Juang Y, Tsao T, Dai Y, Liu H, Chen C, 2007. Exposure assessment of
aluminum arc welding radiation, Health Physics 93(4): 298-306.
36) Marshall WJ, Sliney DH, Lyon TL, Krial NP, Del Valle PF, 1977. Evaluation of the
potential retinal hazards from optical radiation generated by electric welding and cutting
arcs. Aberdeen Proving Ground, MD: U.S. Army Environmental Hygiene Agency
Report, No. 42-0312-77.
37) Okuno T, Ojima J, Saito H, 2010. Blue-light hazard from CO2 arc welding of mild steel,
The Annals of Occupational Hygiene 54(3): 293-298.
Chapter II
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding of
Aluminum Alloys
26
Chapter II
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding of
Aluminum Alloys
Abstract
Ultraviolet radiation (UVR) emitted during arc welding frequently causes
keratoconjunctivitis and erythema. The extent of the hazard of UVR varies depending on
the welding method and conditions. Therefore, it is important to identify the levels of UVR
that are present under various conditions. In this study, I experimentally evaluated the hazard
of UVR emitted in gas tungsten arc welding (GTAW) of aluminum alloys. The degree of
hazard of UVR is measured by the effective irradiance defined in the American Conference
of Governmental Industrial Hygienists guidelines (ACGIH). The effective irradiances
measured in this study are in the range 0.10–0.91 mW/cm2 at a distance of 500 mm from
the welding arc. The maximum allowable exposure times corresponding to these levels are
only 3.3–33 s/day. This demonstrates that unprotected exposure to UVR emitted by GTAW
of aluminum alloys is quite hazardous in practice. In addition, I found the following
properties of the hazard of UVR. (1) It is more hazardous at higher welding currents than at
lower welding currents. (2) It is more hazardous when magnesium is included in the welding
materials than when it is not. (3) The hazard depends on the direction of emission from the
arc.
Key words: hazard, ultraviolet radiation, effective irradiance, gas metal arc welding,
aluminum alloy
2.1 Introduction
The light emitted in arc welding contains strong UVR. In the absence of a barrier, this
Chapter II
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding of
Aluminum Alloys
27
radiation is emitted into the surrounding environment, ensuring that extremely large
numbers of workers at workplaces where arc welding is performed are exposed to UVR.
This includes not only expert arc-welding professionals—whose numbers are estimated at
some 300,000 in Japan—but also welders who do not specialize in arc welding but perform
it occasionally, as well as workers engaged in tasks other than arc welding1).
UVR consists of electromagnetic waves with wavelengths in the range from
approximately 1 to 400 nm2,). However, a precise border between ultraviolet radiation and
visible light cannot be defined, because visual sensation at wavelengths shorter than 400 nm
is noted for very bright sources. The borders necessarily vary with the application3). UVR
is not visible to the human eye. The International Commission on Illumination has
subdivided UVR into three wavelength regimes: UV-A (wavelengths in the range 315–400
nm), UV-B (280–315 nm), and UV-C (100–280 nm)3). Focusing our attention on the
interaction of UVR with the human eye, one finds that UV-C is absorbed by the cornea and
does not reach the interior of the eye. UV-B and UV-A are absorbed mostly by the cornea
and the lens, and only trace amounts (<1%) reach the retina. The portion of the UV spectrum
consisting of wavelengths below approximately 190 nm is known as vacuum UVR; because
this radiation is strongly absorbed by oxygen molecules, it is not transmitted through air.
Because humans are thus not exposed to vacuum UVR—except in extremely rare
circumstances such as low a pressure mercury lamp, a xenon lamp and excimer lasers etc.—
there is little cause for concern regarding its hazard.
UVR interacts strongly with living organisms and is known to cause a variety of
problems4,5). Moreover, UVR is strongly absorbed by proteins and by water; thus, when
UVR is incident on a living organism, the majority of the radiation is absorbed at the surface.
Thus, damage to living organisms due to UVR is confined to surface regions; well-known
examples of acute health effects include keratoconjunctivitis and erythema, while delayed
Chapter II
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding of
Aluminum Alloys
28
health effects include cataracts and skin cancer. In practice, acute health effects due to UVR
occur frequently at workplaces where arc welding is performed1,6). The Japan Welding
Engineering Society surveyed incidences of UV keratoconjunctivitis among workers at
workplaces involving arc welding—including both workers who performed arc welding and
workers who did not1). The results of the survey indicated that as many as 86% of workers
reported past experience with UV keratoconjunctivitis, while 45% reported ongoing
experience with this ailment, with one or more recurrences per month. Moreover, the
majority of arc welders experienced UV keratoconjunctivitis despite wearing welding face
shields. Possible causes for this include (a) cases in which workers fail to put on their face
shields before striking the arc, ensuring exposure to UVR; and (b) cases in which workers
are exposed to UVR by other workers performing arc welding at the same workplaces.
Therefore, these findings demonstrate the need to introduce protective measures at
workplaces involving arc welding to protect workers from UVR. As a basis for designing
such measures, it would be desirable to acquire a quantitative understanding of the hazard
of UVR emitted during arc welding.
The intensity of the UVR emitted during arc welding may be expected to vary
depending on the welding conditions. In particular, it is said that workers experience greater
degrees of sunburn (erythema) during the arc welding of aluminum alloys than in the arc
welding of steel materials, suggesting that the intensity of UVR is greater in this case.
Aluminum and its alloys exhibit excellent properties—including light-weight, high
strength-to-weight ratio, corrosion resistance, workability, and appearance—and are widely
used as raw materials for structural products and components in a wide variety of fields,
including railway vehicles, automobiles, ships, aerospace instruments, and chemical
instruments. Arc welding is used extensively in portions of the production processes for
these aluminum products. The two primary welding methods for aluminum alloys are
Chapter II
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding of
Aluminum Alloys
29
GMAW and GTAW. GMAW is a semi-automatic process in which the wire is supplied
automatically; in this case the shielding gas is taken to be an inert gas, such as argon, helium,
or a mixture of these gases. GTAW is a welding method involving a non-consumable
tungsten electrode; in this method, a filler rod is inserted into a molten pool which is a
localized volume of molten metal in a weld prior to its solidification as weld metal, and an
inert gas is used as the shielding gas. GMAW is primarily used for base metals of thickness
3 mm or greater, while GTAW is used for beams of lesser thickness.
Several previous studies have measured the UVR emitted during arc welding of
aluminum alloys and assessed its hazard with respect to acute health effects5,7-10). The
measurements made by these studies involved only a small, restricted set of welding
conditions and measurement positions. However, the arc welding that takes place at actual
workplaces occurs under a variety of welding conditions, and the situations in which
workers are exposed to the resulting UVR are highly varied as well. In recognition of these
realities at workplaces, it is important to investigate the hazard of the UVR emitted by arc
welding of aluminum alloys under a wide range of conditions.
In this chapter, I conducted investigation of the hazard of UVR emitted during GTAW
of aluminum alloys. In particular, I studied the impact of (i) the type of base metal, the type
of filler rod, and the magnitude of the welding current, (ii) the direction in which UVR is
emitted from the arc, and (iii) the type of electrode.
2.2 Methods
According to the ACGIH guidelines11), the degree of hazard of UVR as a cause of acute
health effects is measured by the effective irradiance. The effective irradiance is defined by
equation (1):
Chapter II
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding of
Aluminum Alloys
30
𝐸𝑒𝑓𝑓 = ∑ 𝐸𝜆・
400
180
𝑆(𝜆)・∆𝜆 ・・・・・(1)
In this equation, Eeff is the effective irradiance (units of W/cm2), Eλ is the spectral irradiance
at wavelength λ (units of W/(cm2 · nm)), S(λ) is the relative spectral effectiveness at
wavelength λ, and Δλ is the wavelength bandwidth (units of nm).
For measurements of UVR, I used the X13 Hazard Lightmeter and a XD-45-HUV UV-
Hazard Detector Head (both from Gigahertz-Optik). These measurement apparatuses were
designed for measuring the effective irradiance. As shown in Figure 2.112), the relative
spectral responsivity of the detector head agrees well with the relative spectral effectiveness
around 270 nm. Some discrepancy between the relative spectral responsivity and the relative
spectral effectiveness is visible from 310 to 320 nm; however, because the relative spectral
effectiveness in this wavelength regime is small (in the range 0.015–0.0010), I expect the
impact of this discrepancy to be small and believe it to cause no difficulties in practice. Thus,
I conclude that this detector head is well-suited to measurements of effective irradiance. In
actual experiments, the measured value displayed by the apparatus is the effective radiant
exposure (units of J/m2). Dividing this value by the measurement time yields the effective
irradiance. The measurement apparatus was calibrated by the manufacturer and was used
within the one-year interval of validity of this calibration.
The position of the welding torch was fixed to keep the arc in the same position, and
the base metal was affixed to a movable table, allowing it to be subject to direct motion to
enable the welding. The distance between the arc and the detector head was set to 500 mm
to mimic actual distances to welders. The measurement time was set to 40 s. To exclude the
time required for the arc to stabilize immediately after welding begins and the time required
for the movable table to accelerate, measurements did not begin until 5 s after the start of
Chapter II
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding of
Aluminum Alloys
31
welding.
Figure 2.1 Relative spectral responsivity of the hazard lightmeter and ACGIH relative
spectral effectiveness.
In this study, no local exhaust ventilation system was used during measurement of
UVR, because local exhaust ventilation is usually not used in the welding workplace. Local
exhaust ventilation may disturb the airflow around the arc, and cause welding defects.
Measurements were repeated three times for each set of conditions and averaged to yield
measured results. Furthermore, following ACGIH guidelines, I divided 3 mJ/cm2 by our
measured values of the effective irradiance to determine the maximum daily exposure time
allowable at that irradiance [equation (2)].
𝑡𝑚𝑎𝑥 =0.003 𝐽 𝑐𝑚2⁄
𝐸𝑒𝑓𝑓 ・・・・(2)
In this equation, tmax is the maximum daily exposure time (units of s) and Eeff is the effective
Chapter II
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding of
Aluminum Alloys
32
irradiance (units of W/cm2).
The welding apparatus was a digital inverter-type pulsed arc welding machine
(DA300P, Daihen Welding and Mechatronics Systems Co., Ltd.) that has been used with
increasing frequency in recent years. The inclination of the welding torch was fixed at 110°.
Using flat position forehand welding, two types of welding were performed: bead-on-plate
welding (in which the base metal is melted while a filler rod is added) and melt-run welding
(in which only the base metal is melted and no filler rod is used). Pure argon was used as
the shielding gas. Other conditions were chosen to match typical welding conditions at
actual workplaces13,14). The primary welding conditions at welding currents of 100 and 200
A are presented in Table 2.1.
Table 2.1 Welding conditions
Welding current, A 100 200
Welding speed, mm/min 200 200
Size of base metal, mm 2 × 300 × 75 5 × 300 × 75
Electrode diameter, mm 2.4 3.2
Electrode extension, mm 4 6
Filler rod diameter, mm 2.4 4.0
Arc length, mm 4 4
Nozzle diameter, mm 16.1 17.2
Shield gas flow rate, l/min 7 8
2.2.1 Impact of the type of base metal, the type of filler rod, and the magnitude of the
welding current
To investigate the impact of the choice of base metal, I conducted melt-run welding—and
measured the resulting UVR—using three base metals specified by the Japanese Industrial
Standards (JIS): A1050P-H24, A5083P-O, and A6061P-T615). Table 2.2 presents the
composition of these base metals as specified by JIS. A1050P-H24 is essentially pure
Chapter II
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding of
Aluminum Alloys
33
aluminum, while A5083P-O is an alloy including 4–5% magnesium and A6061P-T6 is an
alloy including 1% magnesium as well as additional elements other than magnesium. Pure
tungsten was used for the electrode. Welding was performed at a welding current of 200 A.
The detector head was positioned at an angle of 40° from the surface of the base metal and
at an angle of 90° from the welding direction. In addition to the effective irradiance, we also
measured the spectral irradiance of the UVR. The measurement apparatus was a
multichannel spectrometer (HSU-100S, Asahi Spectra Co., Ltd.). The wavelength precision
of the apparatus was ±1.2 nm. The distance from the arc was set to 2600 mm, and the
measurement time was set in the range of 130–235 ms by the automated adjustment
functionality of the measurement apparatus. Further, these measured data not include the
influence of light other than welding arc. This is because, immediately after the
measurement of a welding arc, the measuring apparatus automatically measures the
wavelength distribution of the light under the experimental environment without the
welding arc, and removes the influence other than the welding arc. Figure 2.2 shows a
schematic diagram of experimental setup for measuring effective irradiance and spectral
irradiance.
Table 2.2 Chemical compositions of base metals (mass %)
Element Si Fe Cu Mn Mg Cr Zn Ti V Al
Base metal Thickness, mm
A1050P-H24 2 0.08 0.32 0.02 0.01 0.00 0.01 0.02 0.01 > 99.50
5 0.07 0.34 0.02 0.00 0.00 0.01 0.03 0.01 > 99.50
A5083P-O 2 0.15 0.23 0.03 0.66 4.59 0.11 0.01 0.02 remainder
5 0.15 0.30 0.04 0.58 4.35 0.11 0.02 0.02 remainder
A6061P-T6 2 0.61 0.43 0.28 0.02 1.01 0.23 0.01 0.05 remainder
5 0.62 0.43 0.29 0.02 1.02 0.11 0.01 0.04 remainder
Chapter II
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding of
Aluminum Alloys
34
Figure 2.2 Experimental setup for measuring effective irradiance and spectral irradiance
(schematic diagram).
To investigate the impact of the combination of base metal and filler rod, the bead-on-
plate welding were performed using different types of base metal and filler rod and
measured the UVR in each case. The base metals used were the same three base metals used
for melt-run welding, as discussed above. The bead-on-plate welding is a weld method
applied to surface, as opposed to making a joint, to obtain desired properties or dimensions
(Figure 2.3). For the filler rods, three types of filler rods were used specified by JIS:
A1100BY, A4043BY, and A5183BY16). The JIS-specified composition of these materials is
presented in Table 2.3. A1100BY is essentially pure aluminum, A4043BY is an alloy
containing small quantities of magnesium and other non-magnesium elements, and
A5183BY is an alloy containing 4–5% magnesium. To investigate the impact of the welding
current, two values of the welding current were used: 100 and 200 A. As shown in Figure
2.2, the detector head was positioned at an angle of 40° from the surface of the base metal
and at an angle of 90° from the welding direction. The distance from the arc was 500 mm.
Chapter II
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding of
Aluminum Alloys
35
Table 2.4 presents the combinations of base metals and filler rods, and their symbols.
Table 2.3 Chemical compositions of filler rods (mass %)
Element Si Fe Cu Mn Mg Cr Zn Ti V Al
Filler rods Diameter, mm
A1100BY 2.4 0.04 0.24 0.06 0.00 0.00 > 99.50
4.0 0.05 0.23 0.07 0.00 0.00 > 99.50
A4043BY 2.4 5.14 0.14 0.01 0.00 0.01 0.00 0.02 remainder
4.0 4.97 0.21 0.01 0.01 0.04 0.01 0.03 remainder
A5183BY 2.4 0.07 0.17 0.00 0.70 5.12 0.07 0.00 0.07 remainder
4.0 0.07 0.17 0.00 0.70 5.12 0.07 0.00 0.07 remainder
Table 2.4 Combination of base metal and filler rod
Base metal Filler rod
Symbol JIS designation Importance secondary
element JIS designation
Importance secondary
element
P1 A1050P-H24 (None) Not applicable -
P5 A5083P-O Mg Not applicable -
P6 A6061P-T6 Si Not applicable -
P1F1 A1050P-H24 (None) A1100BY (None)
P5F5 A5083P-O Mg A5183BY Mg
P1F5 A1050P-H24 (None) A5183BY Mg
P5F1 A5083P-O Mg A1100BY (None)
P6F4 A6061P-T6 Si A4043BY Si
2.2.2 Dependence on the direction of emission from the arc
To investigate the dependence on the direction of emission from the arc, I conducted
measurements of UVR while varying the angle from the horizontal surface of the base metal
and the angle with respect to the welding direction. As figure 2.2 illustrates the position of
the detector head, the angle with respect to the welding direction was first fixed at 90°, and
the angle from the surface of the base metal was set to 20°, 30°, 40°, 50°, and 60°. Then the
angle from the surface of the base metal was fixed at 40° and the angle with respect to the
Chapter II
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding of
Aluminum Alloys
36
welding direction was set to 0°, 30°, 60°, and 90°. Melt-run welding was conducted using a
welding current of 200 A and a pure tungsten electrode. The base metal was A5083P-O. The
distance between the detector head and the arc was 500 mm.
Figure 2.3 Bead-on-plate welding (simulated welding with no joint).
2.2.3 Impact of the type of electrode
To investigate the impact of the choice of electrodes, GTAW were performed using five
different JIS-specified electrodes (YWP, YWCe-2, YWLa-2, WZ8, and YWTh-2)17) and
measured the resulting emission of UVR. Table 2.5 presents the composition of these
electrodes as specified by JIS. YWP is a pure tungsten electrode, while the other electrodes
contain oxides. Melt-run welding was performed using a base metal of A5083P-O and a
welding current of 200 A. The detector head was positioned at an angle of 90° from the
welding direction, at an angle of 40° from the surface of the base metal, and at a
measurement distance of 500 mm.
Weld bead
Base metal
Torch
Chapter II
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding of
Aluminum Alloys
37
Table 2.5 Chemical compositions of electrodes (mass %)
Electrodes
(JIS designation)
Chemical compositions
Oxide content Impurities Tungsten
YWP - - ~0.10 > 99.00
YWCe-2 Ce2O3 1.8~2.2 ~0.10 remainder
YWLa-2 La2O3 1.8~2.2 ~0.10 remainder
WZ8 ZrO2 0.7~0.9 ~0.10 remainder
YWTh-2 ThO2 1.7~2.2 ~0.10 remainder
2.3 Results
The effective irradiances measured in this study at a distance of 500 mm from the arc were
in the range 0.09–0.91 mW/cm2. The allowable daily exposure times corresponding to these
values are 3.3–33 s.
Figure 2.4 shows the effective irradiance for various welding materials in melt-run
welding and in bead-on-plate welding. The effective irradiance for melt-run welding was
highest when the base metal was the magnesium-rich P5; lowest values were observed for
P6 (which contains a small amount of magnesium), and still lower values were observed for
P1 (which does not contain any magnesium). Figure 2.5 shows the spectral irradiance of
UVR measured for the case of melt-run welding. For all choices of the base metal, UVR
emission from aluminum was observed at various wavelengths. In the cases of P5 and P6,
intense emission from magnesium was observed at a wavelength near 280 nm.
For the case of bead-on-plate welding, the effective irradiance was highest for the
base-metal/filler-rod combination P5F5, a case in which both the base metal and the filler
rod contain magnesium. The values observed for the combination P1F5—in which only the
filler rod contains magnesium—do not differ significantly from the values observed for the
combination P5F1, in which only the base metal contains magnesium. The lowest value was
observed for the combination P1F1, which consists of pure aluminum; the second lowest
value was observed for the combination P6F4, which contains small amounts of magnesium
Chapter II
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding of
Aluminum Alloys
38
and silicon. A comparison of the P5 case—involving melt-run welding of base metal A5083
P-O—and the P5F5 case, in which bead-on-plate welding was conducted using filler rod
A5183BY—reveals higher values of the effective irradiance for P5. Similarly, a comparison
of P1 and P1F1 reveals higher values of the effective irradiance for the melt-run welding of
P1. For all combinations of base metal and filler rods, the effective irradiance was higher
for a welding current of 200 A than for a welding current of 100 A.
Figure 2.6 shows the effective irradiance for various angles from the horizontal surface
of the base metal. The effective irradiance was greatest when the angle from the surface of
the base metal is 40° and decreased for angles greater or less than this.
Figure 2.7 shows the results of measurements of the effective irradiance versus the
angle of inclination with respect to the welding direction. There was no clear dependence
of the effective irradiance on the angle of inclination.
Figure 2.8 shows the results of measurements of the effective irradiance for different
electrodes. The effective irradiance for electrodes containing oxides was 10–20% larger than
that for the pure tungsten electrode YWP.
Chapter II
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding of
Aluminum Alloys
39
Figure 2.4 Effective irradiance for different base metals and filler rods. Error bar represent
the standard deviation.
Figure 2.5 Spectral irradiance for different base metals in melt-run welding.
Chapter II
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding of
Aluminum Alloys
40
Figure 2.6 Effective irradiance against angle from plate surface. Error bars represent the
standard deviation.
Figure 2.7 Effective irradiance against angle with respect to welding direction. Error bars
represent the standard deviation.
Chapter II
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding of
Aluminum Alloys
41
Figure 2.8 Effective irradiance for different electrodes in melt-run welding. Error bars
represent the standard deviation
2.4 Discussion
The effective irradiances observed at distances of 500 mm from the arc were in the range
0.091–0.91 mW/cm2. At these irradiances, the allowable daily exposure times are just 3.30–
33.0 s, extremely small numbers for the accumulated exposure time over the course of a
single day, meaning that exposure to UVR emitted by GTAW of aluminum alloys is quite
hazardous. It is thought that workers are often exposed to UVR when striking the arc1).
Although the exposure is brief for each strike of arc, this may occur many times because
workers usually strike an arc many times in a day. So, the total exposure time may easily
exceed the allowable daily exposure times obtained in this study. Thus, it is concluded that
if workers are engaged in the GTAW of aluminum alloys without adequate protection, they
are exposed to hazardous quantities of UVR even if they are only welding for short periods
of time.
In this study, no local exhaust ventilation system was used during measurement of
Chapter II
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding of
Aluminum Alloys
42
UVR, because local exhaust ventilation is usually not used in the welding workplace. Local
exhaust ventilation removes the welding fume, which strongly attenuates UVR by scatter
and absorb. Therefore, if local exhaust ventilation had been used during the measurement,
the effective irradiance would have been higher.
Assuming that the effective irradiance of UVR decreases with the distance from the
arc according to the inverse-square law, the allowable daily exposure times at a distance of
5 m from the arc fall in the range 330–3300 s. Thus, even at a distance of 5 m from the arc,
exposure to UVR is hazardous in cases in which the emitted UVR is intense; moreover, even
in cases where the emitted UVR is weak, I sure that prolonged exposure is also hazardous.
Thus, in cases where GTAW of aluminum alloys is performed, it is necessary to take
precautions to ensure that surrounding workers are not exposed to the UVR emitted by the
arc.
For the case of bead-on-plate welding, the effective irradiances measured for a welding
current of 200 A were 2.6–3.6 times greater than those measured for a welding current of
100 A, with other conditions held fixed (Figure 2.4). Thus, the welding current is an
important factor influencing the hazard of the UVR emitted during the welding process; the
hazard of the UVR may be understood to be a rapidly increasing function of the welding
current.
For GTAW of aluminum alloys, the effective irradiance was high for welding materials
containing magnesium (Figure 2.4). For cases P5 and P6, which used base metals A5083P-
O and A6061P-T6, strong emission arising from the presence of magnesium was observed
in the vicinity of 280 nm, while emission from aluminum—the primary component of the
base metals—was observed at wavelengths of 240–260 nm and 300–310 nm (Figure 2.5).
Despite the very low magnesium content of the base metal, its contribution to the spectral
distribution of UVR was on the same order of magnitude as, or even greater than, the
Chapter II
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding of
Aluminum Alloys
43
contribution of aluminum, as shown in the figure. It is able to attribute this to the fact that
the boiling point of magnesium (1090°C) is considerably lower than that of aluminum
(2470°C), ensuring that magnesium is preferentially vaporized from the molten pool, giving
rise to greater UVR. In addition, the relative spectral effectiveness11)—a measure of the
relative hazard of UVR at various wavelengths—was 0.88 at a wavelength of 280 nm, 0.3–
0.65 for wavelengths in the range 240–260 nm, and 0.015–0.3 for wavelengths in the range
300–310 nm. Thus, the impact of aluminum on the effective irradiance is relatively small
compared to that of magnesium. Consequently, it is concluded that the hazard of the UVR
emitted during GTAW of aluminum alloys is primarily determined by the emission from
magnesium. Similar conclusions were obtained from the authors’ previous study of GMAW
of aluminum alloys11).
The effective irradiance of the UVR emitted by GTAW is greatest when the angle from
the surface of the base metal is 40°, and decreases for angles greater or less than this (Figure
2.6). I sure the reason for this to be as follows. Figure 2.9 shows the positional relation
between the nozzle, the simulated arc column and the simulated molten pool, as observed
from the detector. In the figure, a circle shows a simulated molten pool, and the black portion
of the electrode (nozzle) tip displays a simulated arc column. The UVR associated with
GTAW arises from the metal vapor produced from the surface of molten pool18); when the
angle from the surface of the base metal is small, the effective area of the molten pool is
small, but this effective area increases as the angle increases, causing an increase in effective
irradiance. On the other hand, when the angle is too large, the nozzle of the welding torch
covers the molten pool, blocking UVR and reducing the effective irradiance. Thus, when a
welder adopts typical configurations for performing GTAW welding, the UVR will be
strongest near the welder’s head and neck. Welders must take care to protect these areas
thoroughly using welding face shields or other protective gear. In particular, during hot
Chapter II
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding of
Aluminum Alloys
44
summer weather it is common for welders to neglect to equip themselves with protective
gear for the neck region, necessitating heightened attention to the risk of exposure to UVR.
40° 50°
60°
Figure 2.9 Angular relations of nozzle and molten pool observed from the detector
As shown in Figure 2.7, changing the angle with respect to the welding direction yields
essentially no change in the effective irradiance of the UVR emitted in GTAW. In the case
of GMAW, a drop in effective irradiance was observed for directions closer to the welding
direction; this was sure to be caused by absorption or scattering of UVR by fumes (smoke
emitted during welding) produced in GMAW19). The absence of any dependence on the
angle with respect to the welding direction in GTAW may be attributed to the fact that almost
no fumes are produced during this welding process.
The effective irradiances measured for GMAW of aluminum alloys in this study at a
distance of 500 mm from the arc were in the range 0.091–0.91 mW/cm2, while those
measured for GMAW of aluminum alloys in our previous study11) were in the range 0.33–
10.0 mW/cm2, which indicates that the UVR hazard of GTAW is approximately 1/10 that
of GMAW. Both studies investigated the UVR emitted under welding conditions typically
found at actual workplaces. Thus, it is expected that GMAW of aluminum alloys will be
more hazardous than GTAW at actual workplaces, as was observed in research studies.
Chapter II
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding of
Aluminum Alloys
45
2.5 Conclusions
GTAW of aluminum alloys leads to the emission of intense UVR. Exposure to this radiation
is considered hazardous according to the ACGIH guidelines. The hazard of this UVR
exhibits the following characteristics. (1) It is more hazardous at higher welding currents.
(2) It is more hazardous when the welding materials include magnesium. (3) It is more
hazardous for melt-run welding. (4) The hazard depends on the direction of emission from
the arc. (5) Electrodes containing oxides yield stronger hazard than pure tungsten electrodes.
(6) Under the welding conditions typically present at actual workplaces, the hazard of
GTAW is approximately 1/10 that of GMAW.
2.6 References
1) The Japan Welding Engineering Society, 1980. Shakouhogogu no seinouhyouka tou ni
kansuru chousa kenkyu seika houkokusyo, A research report on the performance of eye
protectors against optical radiation, The Japan Welding Engineering Society. (in
Japanese)
2) Japan Standards Association, 2007. The Japan Society for Analytical Chemistry,
Technical terms for analytical chemistry: optical part, JIS K0212, Japan Safety
Appliances Association.
3) International Commission on Illumination, 2011. International lighting vocabulary,
2011, CIE Standard CIE S 017/E: 2011, Vienna, International Commission on
Illumination.
4) World Health Organization Office of Global and Integrated Environmental Health, 1995.
Health and environmental effects of ultraviolet radiation: a summary of Environmental
health criteria 160: ultraviolet radiation, Geneva, World Health Organization.
5) Sliney DH, Wolbarsht M, 1980. Safety with Lasers and Other Optical Sources, New
Chapter II
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding of
Aluminum Alloys
46
York, Plenum press.
6) Emmet EA, Buncher CR, Suskind RB, Rowe KW, 1981. Skin and eye diseases among
arc welders and those exposed to welding operations, Journal of Occupational Medicine
23: 85–90.
7) Lyon TL, Marshall WJ, Sliney DH, Krial NP, Del Valle PF, 1976. Nonionizing radiation
protection special study No. 25-42-0053-77, Evaluation of the potential from actinic
ultraviolet radiation generated by electric welding and cutting arcs, Maryland, US Army
Environmental Hygiene Agency Aberdeen Proving Ground.
8) Okuno T, Kohyama N, Serita F, 2005. Ultraviolet radiation from MIG welding of
aluminum, Safety & Health Digest 51(9): 2-5. (in Japanese)
9) Peng C, Lan C, Juang Y, Tsao T, Dai Y, Liu H, Chen C, 2007. Exposure assessment of
aluminum arc welding radiation, Health Physics 93(4): 298-306.
10) Okuno T, Saito H, Hojo M, Kohyama N, 2005. Hazard evaluation of ultraviolet radiation
emitted by arc welding and other processes, Occupational Health Journal 28(6): 65-71.
(in Japanese)
11) The American Conference of Governmental Industrial Hygienists, 2015. 2015
Threshold limit values for chemical substances and physical agents and biological
exposures indices, Cincinnati, American Conference of Governmental Industrial
Hygienists.
12) Gigahertz-Optik, 2014. X13 Manual, version 12: 14.
13) Yokoo N, Mita T, Watanabe K, 1986. Tigu yousetsu nyumon, Tokyo, Sanpo Publications
Incorporated. (in Japanese).
14) Japan Light Metal Welding Association, 2013. Aluminumu goukin usuita ni okeru
kouryu TIG yousetsu oyobi chokuryu parusu MIG yousetsu no kisotekigihou, Tokyo,
Japan Light Metal Welding Association. (in Japanese).
Chapter II
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding of
Aluminum Alloys
47
15) Japanese Industrial Standards Committee, 2014. Aluminum and aluminum alloy sheets,
strips and plates, JIS H 4000, Japan Standards Association. (in Japanese).
16) Japanese Industrial Standards Committee, 2009. Aluminum and aluminum alloy
welding rods and wires, JIS Z 3232, Japan Standards Association. (in Japanese)
17) Japanese Industrial Standards Committee, 2001. Tungsten electrodes for inert gas
shielded arc welding and for plasma cutting and welding, JIS Z 3233, Japan Standards
Association. (in Japanese).
18) Tsujimura T, Tanaka M, 2012. Numerical simulation of heat source property behavior
in GMA welding, Japan Welding Society 30(1): 68-76. (in Japanese)
19) Nakashima H, Utsunomiya A, Fujii N, Okuno T, 2014. Study of ultraviolet radiation
emitted by MIG welding of aluminum alloys, Journal of light metal welding 52(8): 290-
298. (in Japanese)
Chapter III
Study of Ultraviolet Radiation Emitted by Gas Metal Arc Welding of Aluminum Alloys
48
Chapter III
Study of Ultraviolet Radiation Emitted by Gas Metal Arc Welding of
Aluminum Alloys
Abstract
The ultraviolet radiation (UVR) generated during arc welding is a well-known cause of
photokeratoconjunctivitis and is also associated with dermatitis and skin cancer.
Determining the ultraviolet radiation level of the various welding conditions is important
for establishing protective measures for workers in the workplace.
In this study, the UVR emitted during gas metal arc welding (GMAW) of aluminum
alloys with a digital inverter-type pulsed arc welding machine was measured. In the
experiment, the base metal is moved, and the welding torch and the UVR detector are fixed
to measure the effective irradiance of UVR. Measurements are carried out for 40 seconds
and repeated three times.The distance between the detector and the arc is 500 mm.
The following results were obtained: (1) the effective irradiance of UVR is strongly
influenced by the amount of magnesium contained in aluminum alloys, and magnesium in
the welding wire contributes more to the emission of UVR than that in the base metal; (2)
the effective irradiance is dependent on the angle of the welding direction and the angle
from the base material and is the strongest near the face and cervix of the welding operator;
and (3) the effective irradiance is significantly increased when using the pulsed current.
Key words: ultraviolet radiation, UVR, effective irradiance, GMAW, pulsed current,
aluminum alloys
Chapter III
Study of Ultraviolet Radiation Emitted by Gas Metal Arc Welding of Aluminum Alloys
49
3.1 Introduction
About 15 years ago, a digital inverter-type pulsed arc welding machine (DP welding
machine) was developed. This welding machine has facilitated gas metal arc welding
(GMAW) of aluminum alloys, which are considered difficult to weld. In actual welding
operation, even if the same welding current is used, UVR seems more intense in the GMAW
of aluminum alloys as compared with shielded metal arc welding (SMAW) and CO2 arc
welding of mild steel. Because the opportunities for the GMAW of aluminum alloys are
expected to increase in the future, welding workers and their surrounding workers will be
exposed to strong UVR for longer times in the workplace, and the exposure on the human
body has always been a concern. The effective irradiance during arc welding of aluminum
alloys has been measured in past research1-4). However, in this past research, the effective
irradiance was measured under conditions that were different from those of an actual
welding operation. For example, the measurement time was as short as a few seconds and
the measurement distance was 1 to 2 m, which is longer than that in actual welding
operations. In addition, because the detector was moved along with the arm movements of
the welding operators, the measured values varied. To solve these problems, in this research,
the welding torch was fixed to make the arc remain in the same position, while the base
metal was placed horizontally on a travel device that was moved along a horizontal line at
a constant speed when the effective irradiance was being measured. The measurement
distance was set to 500 mm, and the effective irradiance of the UVR was obtained not only
by using the inverse square method but also by actual measurement.
The effective irradiance during the GMAW of aluminum alloys has been reported to
possibly depend on the magnesium content3). However, it was not clarified whether the
dependence was larger for the magnesium contained in the base metal or that in the welding
wire. To answer this question, I prepared several combinations of base metal and welding
Chapter III
Study of Ultraviolet Radiation Emitted by Gas Metal Arc Welding of Aluminum Alloys
50
wire, measured the effective irradiance, and investigated the effects of magnesium.
Other studies have also reported the angular dependence of the effective irradiance
from the surface of a horizontally arranged base metal5). However, when the UVR exposure
of operators working around the welding site is considered, the angle dependence from the
base metal surface alone is not sufficient. In view of this, this research added studies of the
angle dependence against the welding direction during flat position forehead welding.
In addition, no previous studies have measured the effective irradiance during pulsed
gas metal arc welding (GMAW-P) by the pulsed current of the DP welding machine.
Therefore, I made include this welding process in our study.
In summary, the hazard of the UVR emitted during the GMAW of aluminum alloys
was investigated. In particular, I studied the impact of (i) the type of base metal, the type of
welding wire, and the magnitude of the welding current, (ii) the direction in which the UVR
is emitted from the arc, and (iii) the use of pulsed welding current.
3.2 Hazard assessment of the UVR
According to the American Conference of Governmental Industrial Hygienists (ACGIH)
guidelines6), the degree of hazard of the UVR as a cause of acute health effects is measured
by the effective irradiance. The effective irradiance is defined by equation (1):
𝐸𝑒𝑓𝑓 = ∑ 𝐸𝜆・
400
180
𝑆(𝜆)・∆𝜆 ・・・・・(1)
In this equation, Eeff is the effective irradiance (mW/cm2), Eλ is the spectral irradiance at
wavelength λ (mW/ (cm2·nm)), S(λ) is the relative spectral effectiveness at wavelength λ,
and Δλ is the wavelength bandwidth (nm).
Chapter III
Study of Ultraviolet Radiation Emitted by Gas Metal Arc Welding of Aluminum Alloys
51
ACGIH has set the threshold of Eeff at 270 nm to be limited to 3 mJ/cm2. If the UVR
is irradiated to the skin and eyes unprotected, in general, the maximum exposure time for
the broadband UV source can be determined from equation (2).
𝑡𝑚𝑎𝑥 =3 m J cm2⁄
𝐸𝑒𝑓𝑓 ・・・・・(2)
In this equation, tmax is the maximum daily exposure time (s) and Eeff is the effective
irradiance.
3.3 Methods
For the UVR measurements, An X13 hazard lightmeter and an XD-45-HUV UV-hazard
detector head (both from Gigahertz-Optik) were used. Both of these devices can measure
the effective irradiance conforming to the ACGIH criteria. The detector head has three
sensors. The measurement of effective irradiance was taken by two sensors: one for UV-CB
(measurement wavelength range: 200–320 nm) and one for UV-A (measurement
wavelength range: 320–400 nm). Table 3.1 shows the characteristics of these sensors. The
sensitivity of these sensors was adjusted to coincide with the relative spectral effectiveness
determined by ACGIH and the manufacturer. The measurement device was calibrated by
the manufacturer and used within the one-year validity of the calibration. Figure 2.1 shows
the relation between the relative spectral effectiveness and the sensitivity of the sensors7).
The sensitivity of these sensors almost matches the relative spectral effectiveness in the
vicinity of 270 nm. Some discrepancy between the relative spectral responsivity and the
relative spectral effectiveness is visible from 310 to 320 nm. However, because the relative
spectral effectiveness in this wavelength regime is small (0.015–0.0010), we consider the
influence of this discrepancy to be negligible. Thus, it was concluded that this detector head
Chapter III
Study of Ultraviolet Radiation Emitted by Gas Metal Arc Welding of Aluminum Alloys
52
is well suited to measure the effective irradiance.
Table 3.1 Characteristics of UV sensors
Wavelength, nm Measurement range, mW/cm2 Max. resolution,
mW/cm2
UV-CB 200–320 nm 0.5×10-4–1×103 mW/cm2 5.0×10-6 mW/cm2
UV-A 320–400 nm 0.5×10-7–1 mW/cm2 5.0×10-6 mW/cm2
In this study, in the measurement of the UVR, the position of the welding torch was
fixed to produce arcs in the same position, and the base metal was fixed on a movable table,
which moved the metal linearly for welding. This setup enabled stable measurement. The
distance between the arc and the detector head was set to 500 mm to simulate the actual
distances to welders. The measurement time was set to 40 s. To exclude the time required
for the arc to stabilize immediately after welding began and the time required for the
movable table to accelerate, measurements did not begin until 5 s after the start of welding.
Measurements were repeated three times for each set of conditions and then averaged. In
this study, no local exhaust ventilation system was used during measurement of the UVR,
because local exhaust ventilation is usually not used in welding workplaces (local exhaust
ventilation may disturb the airflow around the arc and cause welding defects).
The welding apparatus was a DP welding machine (DA300P, Daihen Welding and
Mechatronics Systems Co., Ltd.), a machine that has been used with increasing frequency
in recent years. The type of welding was bead-on-plate welding, in which the base metal is
melted while the welding wire is added. The welding was performed by flat position
forehead welding. For the welding wire, we used solid wire of diameter 1.2 mm. The
distance between the base metal and the contact tip was 20 mm, and the wire extension
length before the start of welding was 15 mm. The welding speed was 300 mm/min. The
Chapter III
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53
shielding gas was 100% Ar, and the shielding gas flow rate was 20 l/min. The inner diameter
of the nozzle was 16.5 mm. In this experiment, the effective irradiance was measured during
GMAW-P using the pulsed current. In a DP welding machine, the welding voltage and the
pulse conditions (peak current, peak time, base current, base time) were set by the monistic
setting of the welding current (average current). Table 3.2 shows the pulsed conditions used
in this study. The relation of the welding current and the pulsed conditions are shown in
equation (3).
𝐼𝑎𝑣 =𝐼𝑝𝑇𝑝 + 𝐼𝑏𝑇𝑏
𝑇𝑝 + 𝑇𝑏 ・・・・・(3)
In this equation, Iav: welding current (the average current), Ip: peak current, Tp: peak time,
Ib: base current, Tb: base time.
Table 3.2 Parameters based on welding current in the DP350 welding machine
Welding current (Average current) (A) 100 150 200 250
Welding voltage (V) 19.0 21.5 24.0 26.0
Peak current (A) 330 330 340 370
Base current (A) 30 50 80 120
Peak time (ms) 0.8 0.8 0.8 1.0
3.3.1 Impact of the welding current and the combinations of base metal and welding
wire
To investigate the influence of the welding current and the combinations of base metal and
welding wire, the effective irradiance during bead-on-plate welding was measured. The
welding currents used were 100, 150, 200 and 250 A. For the base metals, we used three
types of base metals specified by the Japanese Industrial Standards (JIS): A1050P-H24,
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54
A5083P-O, and A6063P-O8,9). Table 3.3 presents the composition of these base metals as
specified by JIS. A1100P-O is essentially pure aluminum, A5083P-O is an alloy including
4–5% magnesium and A6063P-O is an alloy including 1% magnesium as well as additional
elements other than magnesium. The dimensions of all base metal were 15 × 300 × 150 mm.
For the welding wires, we used three types of welding wires specified by JIS: A1100WY,
A4043WY, and A5183WY10) The JIS-specified composition of these materials is presented
in Table 3.4. A1100WY is essentially pure aluminum, A4043WY is an alloy containing
small quantities of magnesium and other non-magnesium elements, and A5183WY is an
alloy containing 4–5% magnesium. The diameter of welding wire was 1.2 mm. Table 3.5
lists the combinations of base metal and welding wire, and their abbreviated labels. As
shown in Figure 3.1, the detector head was positioned at an angle of 20° from the surface of
the base metal and at an angle of 90° from the welding direction. The distance from the arc
was 500 mm.
In addition to the effective irradiance, the spectral irradiance of the UVR for
combinations P5W5, P1W1 and P6W4 was also measured. The welding current was 250 A
at that time. By analyzing the intensity of irradiance of each broadband UVR wavelength of
the arc, we can identify the factors that affect the hazard of the UVR. The measurement
apparatus was a multichannel spectrometer (HSU-100S, Asahi Spectra Co., Ltd.). The
wavelength precision of the apparatus was ±1.2 nm. The detector was positioned at an angle
of 5° from the surface of the base metal and at an angle of 90° from the welding direction.
The distance from the arc was set to 2000 mm, and the measurement time was set in the
range of 395 ms by using the automated adjustment functionality of the measurement
apparatus.
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55
Table 3.3 Chemical compositions of base materials (mass%)
Alloy symbol (JIS
designation)
Si Fe Cu Mn Mg Cr Zn Ti Al
A1100-PO min - 0.05 - - - - - 99.00
max 0.90 0.2 0.05 0.10 - -
A5083-PO min - - - 0.40 4.0 0.05 - -
remainder max 0.40 0.40 0.10 1.0 4.9 0.25 0.25 0.15
A6063-PO min 0.20 - - - 0.45 - - -
remainder max 0.6 0.35 0.10 0.10 0.90 0.10 0.10 0.10
Table 3.4 Chemical compositions of welding solid wires (mass%)
Alloy symbol (JIS
designation)
Si Fe Cu Mn Mg Cr Zn Ti Al
A1100-WY min - 0.05 - - - - - 99.00
max 0.90 0.2 0.05 0.10 - -
A4043-WY min 4.5 - - - - - - -
remainder max 6.0 0.8 0.30 0.05 0.05 - 0.10 0.20
A5083-WY min - - - 0.50 4.3 0.05 - -
remainder max 0.40 0.40 0.10 1.0 5.2 0.25 0.25 0.15
Table 3.5 Combinations of base metal and welding solid wire
Combination label Base metal Welding wire
P1W1 A1100P-O A1100WY
P1W5 A1100P-O A5183WY
P5W1 A5083P-O A1100WY
P5W5 A5083P-O A5183WY
P6W4 A6063P-O A4043WY
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56
Figure 3.1 Setup for measuring influence of magnesium in welding materials
(schematic diagram)
3.3.2 Dependence on the direction of emission from the arc
To investigate the dependence on the direction of emission from the arc, we conducted
measurements of the UVR while varying the angle from the horizontal surface of the base
metal and the angle in the welding direction. Figures 3.2 and 3.3 illustrate the position of
the detector head. The angle with respect to the welding direction was first fixed at 90°, and
the angle from the surface of the base metal was set to 20°, 30°, 40°, 50°, and 60°. Then the
angle from the surface of the base metal was fixed at 50° and the angle with respect to the
welding direction was set to 0°, 30°, 60°, and 90°. Bead-on-plate welding was conducted
by using welding currents of 100, 150, 200 and 250A. The base metal was A5083P-O and
the welding wire was A5183WY. The distance between the detector head and the arc was
500 mm.
Chapter III
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57
Figure 3.2 Setup for measuring angle dependence from the material surface (schematic
diagram)
Figure 3.3 Setup for measuring angle dependence of the welding direction (schematic
diagram)
Chapter III
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58
3.3.3 Influence of the pulsed current
To investigate the influence of the pulsed current (GMAW-P) on the effective irradiance,
the effective irradiance of the GMAW of the steady welding current (GMAW-S) was
measured. Table 3.6 shows the welding parameters including current and voltage in GMAW-
S. The bead-on-plate welding was performed using the base metal A5083P-O (t30×400×250
mm) and welding wire A5183-WY. As shown in Figure 3.3, the detector head was
positioned at an angle of 50° from the surface of the base metal and at an angle of 90° from
the welding direction. The distance from the arc was 500 mm.
Table 3.6 Welding parameters of GMAW-S
Welding current (A) 100 150 200 250
Welding voltage (V) 14.0 16.0 23.5 26.5
3.4 Results
The effective irradiances measured in this study at a distance of 500 mm from the arc were
in the range of 0.30–10 mW/cm2. The allowable daily exposure times corresponding to these
values are 0.30–10 s.
Figure 3.4 shows the effective irradiance for different combinations of base metal and
welding wire. In all combinations, the effective irradiance increases with increasing welding
current. The effective irradiance is highest for the combination P5W5, in which both the
base metal and the welding wire contained magnesium. The lowest value is observed for the
combination P6W4, in which both the base metal and the welding wire contained small
amounts of magnesium and silicon. The next lowest value is observed for the combination
P1W1, in which both the base metal and the welding wire consisted of pure aluminum.
Figure 3.5 shows the effective irradiance for various angles from the horizontal surface
of the base metal. The effective irradiance is highest when the angle from the surface of the
Chapter III
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59
base metal is 50° and decreases for angles greater or less than this.
Figure 3.6 shows the effective irradiance and the angle of inclination with respect to
the welding direction. The effective irradiance is highest when the angle from the welding
direction is 60°, and lowest when the angle is 30°.
Figure 3.7 shows the effective irradiance of the UVR emitted during GMAW. The
aluminum alloys are strongly influenced by the pulsed current. The effective irradiance
measured for GMAW-P using the pulsed current is 3.3–9.7 mW/cm2 in the welding current
range of 100–250 A. On the other hand, the effective irradiance measured for GMAW-S
using the steady current is 3.1–10.0 mW/cm2 in the welding current range of 150–250 A.
Figure 3.4 Relation of effective irradiance and combinations of wire and base metal
Chapter III
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60
Figure 3.5 Relation of effective irradiance at 500 mm and horizontal angle from base metal
surface at arc
Figure 3.6 Relation of effective irradiance at 500 mm and angle from welding direction at
arc
Chapter III
Study of Ultraviolet Radiation Emitted by Gas Metal Arc Welding of Aluminum Alloys
61
Figure 3.7 Relation of effective irradiance and pulsed and steady current control systems
3.5 Discussion
The effective irradiance observed at a distance of 500 mm from the arc was in the range of
0.30–10 mW/cm2. At these irradiances, the allowable daily exposure times are just 0.30–10
s, which are extremely short times. These results indicate that the exposure to the UVR
emitted by the GMAW of aluminum alloys is quite hazardous. It is thought that workers are
often exposed to UVR when the arc is started1). Although the exposure is brief for each start
of an arc, the exposure can occur often because workers usually start an arc many times in
a day. Therefore, the actual total exposure time can easily exceed the allowable daily
exposure times determined in this study. Thus, it is concluded that if workers engage in the
GMAW of aluminum alloys without adequate protection, they are exposed to hazardous
quantities of the UVR for short periods of time. Assuming that the effective irradiance of
the UVR decreases as the inverse square low of distance. At that time, the calculated
allowable exposure time per 8 hours a day when there is no shielding between the welding
arc and the irradiated surface of the UVR and the irradiated surface does not move is shown
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62
in Figure 3.8. Assuming a working hour of 8 hours, the distance between a welding arc and
a worker, which is calculated from the effective irradiance measured in this chapter and
must be kept in order to avoid the acute health effects of UVR, is 28–150 m. However,
welding arcs do not occur continuously for 8 hours in workplaces, and a worker's UVR-
irradiated skin is moving. Therefore, the calculated distance between a welding arc and a
worker is a minimum value, which is considered to be longer in practice. For example, the
allowable daily exposure times at a distance of 5 m from the arc will be in the range of 30–
1000 s. Thus, even at a distance of 5 m from the arc, exposure to the UVR is hazardous in
cases in which the emitted UVR is intense. Moreover, even in cases in which the emitted
UVR is weak, I sure that prolonged exposure is hazardous. Thus, in cases where the GMAW
of aluminum alloys is performed, it is necessary to take precautionary measures to ensure
that surrounding workers are not exposed to the UVR emitted by the arc.
Figure 3.8. Allowable exposure time per day and distance from welding arc
Chapter III
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63
3.5.1 Impact of the magnitude of the welding current and the combinations of base
metal and welding wire
The effective irradiance measured in this study, regardless of pulsed or steady current and
the combination of base metals and welding wires, increased with increasing welding
current (Figure 3.4 and Figure 3.7). This trend was also previously observed for the GMAW
of mild steel5,11) and the GTAW of aluminum alloys12). Thus, the welding current is an
important factor that influences the degree of hazard of the UVR emitted during the welding
process; that is, the UVR hazard can be understood to be a rapidly increasing function of
the welding current.
The effective irradiance was highest for P5W5, in which both the base metal and the
welding wire contained magnesium. The effective irradiance was low for the combination
P1W1 consisting of pure aluminum and P6W4 containing small amounts of magnesium and
silicon. Figure 3.9 shows the spectral irradiance of the UVR measured for the cases of P1W1,
P5W5 and P6W4. For P5W5, strong emission due to the presence of magnesium was
observed in the vicinity of 280 nm. For all combinations, emission from aluminum, which
was the primary component of the base metals, was observed at wavelengths of 240–260
nm and 300–310 nm. The relative spectral effectiveness6), which is a measure of the relative
hazard of UVR at various wavelengths, was 0.88 at a wavelength of 280 nm, 0.3–0.65 for
wavelengths in the range 240–260 nm, and 0.015–0.3 for wavelengths in the range 300–310
nm. Thus, the impact of aluminum on the effective irradiance is relatively small compared
to that of magnesium. Consequently, we conclude that the hazard of the UVR emitted during
GMAW of aluminum alloys is primarily determined by the emission from magnesium.
Similar conclusions were obtained from the previous study of GMAW of aluminum alloys3).
However, the research of Okuno et al.3) does not clarify which case has the large
dependence: the case in which magnesium is contained in the base metal, and the case in
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64
which magnesium is contained in the welding wire. Therefore, we compared P1W5 in which
only the welding wire contained magnesium and P5W1 in which only the base metal
contained magnesium. As a result, the effective irradiance for P1W5 was 3 to 4 times higher
than that for P5W1 (Figure 3.4). We attribute this to the fact that the boiling point of
magnesium (1090°C) is considerably lower than that of aluminum (2470°C). This difference
in boiling points ensures that magnesium is preferentially vaporized from the welding wire
and thus gives rise to stronger emissions. Therefore, the effective irradiance that is emitted
during arc welding is strongly dependent on the elements contained in the wire. Furthermore,
magnesium contained in the welding wire has strong effect.
Figure 3.9 Relation of spectral irradiance and combinations of base metal and welding wire
3.5.2 Dependence on the direction of emission from the arc
The effective irradiance is highest when the angle from the surface of the base metal is 50°,
and decreases for angles greater or less than 50° (Figure 3.5). Figure 3.10 shows the
positional relation between the nozzle, the simulated arc column and the simulated molten
Chapter III
Study of Ultraviolet Radiation Emitted by Gas Metal Arc Welding of Aluminum Alloys
65
pool, as observed from the detector. In the figure, the concentric circles show a simulated
molten pool, and the black portion of the wire tip displays a simulated arc column. The UVR
is emitted from around the arc column, but the apparent area of the simulated arc column
decreases with the increasing angle of the detector. In contrast, the apparent area of the
simulated molten pool increases with the increasing angle of the detector. Thus, it is
considered that the reflected UVR from the molten pool is detected. In addition, it is
presumed that the effective irradiance decreases when the apparent area of the arc column
and molten pool are decreased by hiding the nozzle and the detector angle is 60° and more.
In previous studies of Okuno et al.3) for the GMAW of mild steel, the effective irradiance
was reported to have a maximum value at an angle of 50°–60°. The slight angle difference
between that study and the present study is considered to have influenced the wire extension
length. The wire extension length in the Okuno et al. study was the same (15 mm) as that in
this study. However, in the GMAW of aluminum alloys, a contact chip is located on the
inner side of the nozzle tip, whereas in GMAW of mild steel, the positions of the tip of the
contact chip and the nozzle tip are the same. If the wire extension length is the same, the
distance between the nozzle tip and the base metal in the GMAW of aluminum alloys
becomes closer as compared to the GMAW of mild steel. In addition, the diameter of the
nozzle used in the GMAW of aluminum alloys is larger than that used in the GMAW of mild
steel. Therefore, a molten pool is easily obscured by the nozzle, and it is believed that the
effective irradiance is reduced at 60°. It is considered that the angular dependence from the
surface of the base metal is affected by the wire extension length and the nozzle diameter.
The effective irradiance was high at welding direction angles of 60° and 90°, and was
found to depend on the angle of the welding direction (Figure 3.6). The reason that the
effective irradiance decreased according the welding direction is thought to be absorption
and scattering of the UVR by fumes that flowed toward the welding direction because the
Chapter III
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66
welding torch was inclined in the welding direction.
As shows in figure 3.11, from the results of the two kinds of angle dependence of the
effective irradiance, the hazard of the UVR around neck of the welding worker is the
strongest in flat position forehead welding. The allowable exposure time obtained from
equation (2) is 0.34 s when the welding current is 200 A. Therefore, the welding operator
must fully safeguard himself with protective equipment such as a face shield.
40° 50°
60°
Figure 3.10 Angular relations of nozzle and molten pool observed from the detector
Figure 3.11 General welding position of GMAW at flat forehead welding
3.5.3 Influence of pulsed current
In the GMAW-S when the welding current was 100 A, the arc was not stabilized, and an
Welding direction 50°
Chapter III
Study of Ultraviolet Radiation Emitted by Gas Metal Arc Welding of Aluminum Alloys
67
appropriate welding bead was not formed, so the data of 100 A was excluded. The effective
irradiance measured in this study, regardless of the pulsed current, increased with increasing
welding current. At the welding current of 200 A or less, the effective irradiance was higher
in GMAW-P than in GMAW-S, but the effective irradiance for both was approximately the
same at welding current of 250 A (Figure 3.7).
Figure 3.12 shows photographs of the wire tip for welding at a welding current of 150
A. Figure 3.12 (a) shows the wire tip during the GMAW-S. The shape of the tip stabilized
in this state regardless of the passage of time, and the arc was continuously generated.
Figures 3.12 (b) and (c) show the tip during the GMAW-P. Figure 3.12 (b) shows the aspect
of the wire tip at the time of energizing the base current. Because the light emission of the
arc is weak, and the molten metal has just migrated to the molten pool, the wire tip is sharp.
Figure 3.12 (c) shows the aspect of the wire tip at the time of energizing the peak current.
The welding arc is strong. The tip of the wire is melted by the arc thermal and its shape is
dull. With the passage of time, the condition of the tip of the wire in (b) and (c) is repeated,
and so the droplet transfer of GMAW-P is a spray transfer due to the pulsed current. Figure
3.13 shows the welding bead at 150 A. The weld bead formed by GMAW-P has uniform
corrugation, smoothness and good compatibility with the base metal. On the other hand, the
welding bead formed by GMAW-S has bead unevenness and slight meandering. It can be
inferred that the difference in the transfer mode of the droplet was due to the presence or
absence of the pulsed current. A similar tendency was observed also with a welding current
of 200 A. Figure 3.14 shows the change in welding currents between GMAW-S and GMAW-
P at 150 A. In GMAW-P, welding voltage and unit pulse conditions (peak current, peak time,
base current, base time) are unitarily controlled by setting the welding current (average
current). In the pulsed current, a strong welding arc is generated while the peak current is
applied, and the welding arc becomes weak while the base current is applied. As shown in
Chapter III
Study of Ultraviolet Radiation Emitted by Gas Metal Arc Welding of Aluminum Alloys
68
Table 3.2, the peak current is nearly constant regardless of the welding current. Therefore,
the factor affecting the effective irradiance is the peak current time or the base current time,
that is, the factor affecting the effective irradiance is considered to be the pulsed current. On
the other hand, in GMAW-S, the welding current hardly changes and an arc is continuously
generated. In GMAW, the welding current is an important factor affecting effective
irradiance, as is evident from previous studies1-5,11,12). Therefore, it is assumed that the
difference in the increasing tendency of the effective irradiance is due to the difference in
the transfer mode of the droplet when using the pulsed current (Figure 3.7).
(a) (b) (c)
GMAW-S GMAW-P GMAW-P
Figure 3.12 State of wire tip at 150 A welding current
Figure 3.13 Shape of bead at 150 A welding current
Welding wire Welding wire Welding wire
GMAW-P
GMAW-S
Chapter III
Study of Ultraviolet Radiation Emitted by Gas Metal Arc Welding of Aluminum Alloys
69
Figure 3.14 Relation of welding current and welding time at 150 A
On the other hand, at welding current of 250 A, as shown in Figure 3.15, in both
GMAW-S and GMAW-P, the transfer mode of the droplets was the same as spray transfer.
In addition, as shown in Figure 3.16, the weld bead shape after welding was almost the same.
Therefore, since the welding result and the molten droplet transition form are the same, the
effective irradiance is considered to become approximately the same value.
(a) (b) (c) (d)
GMAW-S GMAW-P
Fig 3.15 State of wire tip of at 250 A welding current
Chapter III
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70
Fig. 3.16 Shape of bead at 250 A welding current
3.6 Conclusions
GMAW of aluminum alloys leads to the emission of intense UVR. Exposure to this radiation
is considered hazardous according to ACGIH guidelines. The hazard of UVR exhibits the
following characteristics. (1) It is more hazardous at higher welding currents. (2) It is more
hazardous when the welding materials include magnesium. In particular, the hazard of UVR
becomes stronger when the welding wire contains magnesium. (3) The hazard depends on
the direction of emission from the arc. (4) It is more hazardous for pulsed welding currents
than for steady welding currents.
3.7 References
1) Sliney DH, Wolbarsht M, 1980. Safety with Lasers and Other Optical Sources, New
York, Plenum press.
2) Lyon TL, Marshall WJ, Sliney DH, Krial NP, Del Valle PF, 1976. Nonionizing radiation
protection special study No. 42-0053-77, Evaluation of the potential from actinic
ultraviolet radiation generated by electric welding and cutting arcs, US Army
GMAW-P
GMAW-S
Chapter III
Study of Ultraviolet Radiation Emitted by Gas Metal Arc Welding of Aluminum Alloys
71
Environmental Hygiene Agency Aberdeen Proving Ground ADA033768, Maryland.
3) Okuno T, Kohyama N, Serita F, 2005. Ultraviolet radiation from MIG welding of
aluminum, Safety & Health Digest 51(9): 2-5. (in Japanese)
4) Peng C, Lan C, Juang Y, Tsao T, Dai Y, Liu H, Chen C, 2007. Exposure assessment of
aluminum arc welding radiation, Health Physics 93(4): 298-306.
5) Okuno T, Ojima J, Saito, H, 2001. Ultraviolet radiation emitted by CO2 arc welding, The
Annals of Occupational Hygiene 45(7): 597–601.
6) The American Conference of Governmental Industrial Hygienists, 2015. 2015
Threshold limit values for chemical substances and physical agents and biological
exposures indices, Cincinnati, American Conference of Governmental Industrial
Hygienists.
7) Gigahertz-Optik, 2014. X13 Manual, version 12: 14.
8) Japanese Industrial Standards Committee, 2014. Aluminum and aluminum alloy sheets,
strips and plates, JIS H 4000, Japan Standards Association. (in Japanese).
9) Japanese Industrial Standards Committee, 2015. Aluminum and aluminum alloy bars
and wires, JIS H 4040, Japan Standards Association. (in Japanese).
10) Japanese Industrial Standards Committee, 2009. Aluminum and aluminum alloy
welding rods and wires, JIS Z 3232, Japan Standards Association. (in Japanese)
11) Nakashima H, Utsunomiya A, Takahashi J, Fujii N, Okuno T, 2016. Hazard of ultraviolet
radiation emitted in gas metal arc welding of mild steel, Journal of Occupational Health
58(5): 452-459.
12) Nakashima H, Utsunomiya A, Fujii N, Okuno T, 2016. Hazard of ultraviolet radiation
emitted in gas tungsten arc welding of aluminum alloys, Industrial Health 54(2): 149–
159.
Chapter IV
Hazard of Ultraviolet Radiation Emitted in Gas Metal Arc Welding of Mild Steel
72
Chapter IV
Hazard of Ultraviolet Radiation Emitted in Gas Metal Arc Welding of
Mild Steel
Abstract
Ultraviolet radiation (UVR) emitted during arc welding frequently causes
keratoconjunctivitis and erythema in the workplace. The degree of hazard from UVR
exposure depends on the welding method and conditions. Therefore, it is important to
identify the UVR levels present under various conditions. The UVR levels emitted in gas
metal arc welding (GMAW) of mild steel were experimentally evaluated. For welding
current, two types welding current were used of a pulsed current and a steady current. The
shielding gases were 80% Ar + 20% CO2 and 100% CO2. The effective irradiance defined
in the American Conference of Governmental Industrial Hygienists guidelines was used to
quantify the UVR hazard. The effective irradiance measured in this study was in the range
of 0.51–12.9 mW/cm2 at a distance of 500 mm from the arc. The maximum allowable
exposure times at these levels are only 0.23–5.9 s/day. The following conclusions were
made regarding the degree of hazard from UVR exposure during the GMAW of mild steel:
(1) It is more hazardous at higher welding currents than at lower welding currents. (2) At
higher welding currents, it is more hazardous when 80% Ar + 20% CO2 is used as a shielding
gas than when 100% CO2 is used. (3) It is more hazardous for pulsed welding currents than
for steady welding currents. (4) It appears to be very hazardous when metal transfer is the
spray type. This study demonstrates that unprotected exposure to UVR emitted by the
GMAW of mild steel is quite hazardous.
Keywords: effective irradiance, gas metal arc welding, hazard, mild steel, ultraviolet
Chapter IV
Hazard of Ultraviolet Radiation Emitted in Gas Metal Arc Welding of Mild Steel
73
radiation
4.1 Introduction
The light emitted during arc welding contains intense UVR. In the absence of a barrier, this
radiation is emitted into the surrounding environment, and as a result, extremely large
number of workers at workplaces where arc welding is performed are exposed to UVR. This
includes not only expert arc-welding professionals, whose numbers are estimated at 350,000
in Japan, but also welders who perform arc welding occasionally and workers engaged in
tasks other than arc welding1). UVR refers to electromagnetic waves in the range of ~1–400
nm2). However, a precise border between UVR and visible light cannot be defined because
visual sensations from very bright sources are experienced at wavelengths below 400 nm.
Therefore, the borders necessarily vary from situation to situation 3). UVR below
approximately 190 nm is known as vacuum UVR because it is strongly absorbed by oxygen
molecules and therefore cannot propagate through air.
UVR is emitted during arc welding over its entire wavelength range excluding vacuum
UVR, although the wavelength distribution of UV differs depending on the welding
conditions 4,5). UVR from the arc welding of steel consists mostly of a large number of
spectral lines of iron scattered over this wavelength range.
UVR is known to cause a variety of problems6,7). For example, because it is strongly
absorbed by proteins and water, UVR incident on a living organism is primarily absorbed
at the surface, causing damage confined to surface regions. Well-known examples of acute
health effects include keratoconjunctivitis and erythema, whereas delayed health effects
include cataracts and skin cancer. In practice, such acute health effects because of UVR
occur frequently at workplaces where arc welding is performed1). The Japan Welding
Engineering Society surveyed incidences of UV keratoconjunctivitis among 1667 workers
Chapter IV
Hazard of Ultraviolet Radiation Emitted in Gas Metal Arc Welding of Mild Steel
74
at 47 workplaces where arc welding is performed; the survey included workers who
performed arc welding as well as workers who did not1). The results indicated that as many
as 86% of the workers reported past experience with symptoms of UV keratoconjunctivitis,
including foreign body sensation, ophthalmalgia, lacrimation, and photophobia, whereas
45% reported ongoing experience with this ailment with one or more recurrences per month
even though the majority of arc welders who experienced UV keratoconjunctivitis wore
welding face shields. Possible causes for this include (a) cases in which workers mistakenly
put on their face shields after starting the arc instead of immediately before thus exposing
themselves to UVR and (b) cases in which workers were exposed to UVR by co-workers
performing arc welding nearby. In addition, in a survey by Emmett et al.7), 92% of welders
had suffered one or more flash burns (keratoconjunctivitis), and 40% were afflicted with
erythema in the neck.
These findings demonstrate the need to introduce protective measures at workplaces
that use arc welding to protect all workers from UVR. As the basis for designing such
measures, it is desirable to obtain a quantitative understanding of the hazard of UVR emitted
during arc welding. In an actual work site, arc welding is performed under a variety of
conditions, and the degree of hazard of the emitted UVR is thought to differ for each
condition. Therefore, it is necessary to examine the hazards of the UVR emitted during arc
welding under various conditions.
Arc welding of metallic materials is conducted primarily on mild steel, aluminum
alloys, and stainless-steel alloys. GMAW, which uses a continuously fed consumable
electrode and a shielding gas, is most often used for mild steel. GMAW is conducted while
covering the welding point and the arc by the shielding gas. The shielding gas prevents a
decrease in welding quality, such as the formation of an oxide or nitride because of exposure
of the weld metal to air. The GMAW electrode is a coiled consumable wire that is
Chapter IV
Hazard of Ultraviolet Radiation Emitted in Gas Metal Arc Welding of Mild Steel
75
automatically supplied throughout the welding. A few previous studies have measured the
UVR emitted during arc welding processes, such as the GMAW of mild steel, and assessed
their acute health effects4,5,8). However, in these studies, detailed information on the actual
welding was not provided. Therefore, the available data about the level of UVR emitted by
GMAW is unreliable and insufficient. In particular, the effects of specific conditions have
not been examined systematically. One of the authors of this paper performed GMAW using
100% CO2 in experiments and examined in detail the UVR emitted under these conditions9).
It was clearly found that the UVR hazard tends to increase with welding current and is
dependent on the type of welding wire.
In this study, the UVR hazard present during the GMAW of mild steel were
investigated using a shielding gas of 80% Ar + 20% CO2 or 100% CO2 that are most
frequently used in arc welding of mild steel in Japan. The UVR emitted during GMAW
performed with the recently popular digital inverter-type pulsed arc welding machine was
measured, and its acute health effects were assessed in accordance with the American
Conference of Governmental Industrial Hygienists (ACGIH) guidelines10). In particular, I
studied the influence of (i) the type of shielding gas and the magnitude of the welding
current, and (ii) using pulsed vs. steady welding current.
4.2 Methods
According to the ACGIH guidelines, the degree of URV hazard as a cause of acute health
effects is measured by the effective irradiance. The effective irradiance is defined by
Chapter IV
Hazard of Ultraviolet Radiation Emitted in Gas Metal Arc Welding of Mild Steel
76
where Eeff is the effective irradiance (mW/cm2), Eλ is the spectral irradiance at wavelength
λ (mW/(cm2 · nm)), S(λ) is the relative spectral effectiveness at wavelength λ, and Δλ is
the bandwidth (nm).
For the UVR measurements, an X13 hazard lightmeter and an XD-45-HUV UV-hazard
detector head (both from Gigahertz-Optik) were used, which are designed for measuring
effective irradiance. The relative spectral responsivity of the detector head agrees well with
the relative spectral effectiveness around 270 nm11). Some discrepancy between the relative
spectral responsivity and the relative spectral effectiveness is visible from 310 to 320 nm.
However, because the relative spectral effectiveness in this wavelength regime is small
(0.015–0.0010), I consider the influence of this discrepancy to be too small to cause issues
in practice. Thus, it was concluded that this detector head is well suited to measure the
effective irradiance. In actual experiments, the value measured by the devices is the effective
radiant exposure (J/m2). Dividing this value by the measurement time yields the effective
irradiance. The measurement device was calibrated by the manufacturer and used within the
one-year validity of the calibration.
The position of the welding torch was fixed to produce arcs in the same position, and
the base metal was fixed on a movable table, which moved the metal for welding. The
distance between the arc and the detector head was set to 500 mm to mimic the actual
distances to welders. In addition, the detector head was positioned at an angle of 40° from
the surface of the base metal and at an angle of 90° from the welding direction. Figure 4.1
displays a schematic diagram of our experimental setup for measuring effective irradiance.
The measurement time was set to 40 s. To exclude the time required for the arc to stabilize
immediately after welding begins and the time required for the movable table to accelerate,
measurements did not begin until 5 s after the start of welding. In this study, no local exhaust
ventilation system was used during the measurement of UVR because local exhaust
Chapter IV
Hazard of Ultraviolet Radiation Emitted in Gas Metal Arc Welding of Mild Steel
77
ventilation is usually not used in welding workplaces (local exhaust ventilation may disturb
the airflow around the arc and cause welding defects).
Measurements were repeated three times for each set of conditions and then averaged.
Furthermore, following the ACGIH guidelines, 3 mJ/cm2 was divided by our measured
values of effective irradiance to determine the maximum daily exposure time allowable at
that irradiance (equation (2)).
In this equation, tmax is the maximum daily exposure time (s) and Eeff is the effective
irradiance.
The effective irradiance of the UVR emitted during three types of welding were
measured: 100% CO2 welding (using steady welding current), steady 80% Ar + 20% CO2
welding and pulsed 80% Ar + CO2 welding.
The welding apparatus was a digital inverter-type pulsed arc welding machine (DP350,
DAIHEN Welding and Mechatronics Systems Co., Ltd.), which has recently become
popular. The inclination of the welding torch was fixed at 110°. The type of welding was
bead-on-plate welding in which the base metal is melted while the welding wire is added.
The welding was performed using flat position forehead welding. The base metal was rolled
SS400, which is a mild structural steel specified by the Japanese Industrial Standards (JIS)
12). The dimensions of the base material were 30 mm × 380 mm × 50 mm. For the welding
wire, a solid wire YGW12 of diameter 1.2 mm specified by JIS13) was used. The usable
range of welding current for this wire was 80–350 A for flat position welding. The welding
speed was 300 mm/min. The shielding gas was 80% Ar + 20% CO2 or 100% CO2, and the
shielding gas flow rate was 15 l/min. The distance between the base metal and the contact
Chapter IV
Hazard of Ultraviolet Radiation Emitted in Gas Metal Arc Welding of Mild Steel
78
tip was 17 mm, and the wire extension length before the start of welding was 12 mm. The
welding parameters are listed in Table 4.1. Here the welding voltages were preset values
corresponding to the welding current determined by the manufacturer of the welding
equipment.
Fig. 4.1 Experimental setup for measuring effective irradiance (schematic diagram)
4.2.1 Influence of the type of shielding gas and the magnitude of the welding current
To investigate the influence of the type of shielding gas, I conducted bead-on-plate welding
and measured the resulting UVR when using 80% Ar + 20% CO2 or 100% CO2 as the
shielding gas and using steady welding current. The range of the welding current was 100–
350 A as shown in Table 4.1. Because it is less expensive, 100% CO2 is used more
commonly as shielding gas in the GMAW of mild steel in Japan, whereas mixed gas is
usually used when manufacturing high-quality products efficiently.
4.2.2 Influence of pulsed current
In order to investigate the influence of pulsed current, the pulsed 80% Ar + CO2 welding
Chapter IV
Hazard of Ultraviolet Radiation Emitted in Gas Metal Arc Welding of Mild Steel
79
was performed and the resultant UVR was measured. Then it compared it with the results
for steady 80% Ar + 20% CO2 welding. Incidentally, the digital inverter-type pulsed arc
welding machine provides excellent stability of the arc in the low current range, highly
effective reduction of sputter, and is mainly used under 250 A. Therefore, the range of
welding current used was 100–250 A as shown in Table 4.1. The pulsed current is now
commonly used in the welding of thin plates of automobile bodies.
Table 4.1 Welding parameters of 100% CO2, steady 80% Ar+20% CO2 welding and
pulsed 80% Ar+20% CO2 welding
100% CO2
Welding current, A
(Steady)
100
150
200
250
300
350
Welding voltage, V 18.5 19.0 23.0 27.0 34.0 38.0
Steady
80%Ar+20%CO2
Welding current, A
(Steady)
100
150
200
250
300
350
Welding voltage, V 16.0 17.0 20.0 26.5 33.0 35.5
Pulsed
80%Ar+20%CO2
Welding current, A
(Average)
(Peak / Base)
100
(450/35.0)
150
(450/44.0)
200
(450/55.0)
250
(450/60.0)
- -
Time (Peak / Base), s (1.4/7.5) (1.4/4.0) (1.6/2.8) (1.8/1.9) - -
Welding voltage, V 21.3 23.3 25.5 28.1 - -
4.3 Results
Figures 4.2 and 4.3 display the effective irradiance for various welding conditions in bead-
on-plate welding. The effective irradiance measured in this study at a distance of 500 mm
from the arc was in the range of 0.51–12.9 mW/cm2. The allowable daily exposure times
corresponding to these values are 0.23–5.9 s.
Figure 4.2 shows that the effective irradiance in bead-on-plate welding of mild steel
was influenced by the welding current and the shielding gas composition. The effective
irradiance increased with increasing welding current for each type of shielding gas. For the
Chapter IV
Hazard of Ultraviolet Radiation Emitted in Gas Metal Arc Welding of Mild Steel
80
case of steady 80% Ar + 20% CO2 welding, the effective irradiance measured with welding
currents of 100–350 A was in the range of 0.51–12.9 mW/cm2. The increase in effective
irradiance between current intervals is very large, starting from 250 A. For 100% CO2
welding, the effective irradiance measured with welding currents of 100–350 A was in the
range of 0.69–7.4 mW/cm2. The effective irradiances measured with steady 80% Ar + 20%
CO2 welding and 100% CO2 welding at 250 A or less were approximately equal. However,
at 300 A and higher, the effective irradiance for steady 80% Ar + 20% CO2 welding
increased beyond that for 100% CO2 welding.
Fig. 4.2 Effective irradiance for 100% CO2 welding and steady 80% Ar + 20% CO2 welding.
Measurements were repeated three times for each set of conditions and then averaged.
As shown in Figure 4.3, the effective irradiance of UVR emitted during mild steel
arc welding was strongly influenced by the pulsed current. The effective irradiance
measured for pulsed 80% Ar + 20% CO2 welding with welding currents of 100–250 A was
in the range of 3.4–11.6 mW/cm2. The effective irradiance increased with increasing
Chapter IV
Hazard of Ultraviolet Radiation Emitted in Gas Metal Arc Welding of Mild Steel
81
welding current. In addition, the effective irradiance of UVR occurring during pulsed 80%
Ar + 20% CO2 welding was very high in comparison with that during steady 80% Ar + 20%
CO2 welding.
Fig. 4.3 Effective irradiance for steady and pulsed 80% Ar+20% CO2 welding.
Measurements were repeated three times for each set of conditions and then averaged.
4.4 Discussion
The effective irradiance observed at a distance of 500 mm from the arc was in the range of
0.51–12.9 mW/cm2. At these irradiances, the allowable daily exposure times are just 0.23–
5.9 s, which are extremely short times. These results indicate that the exposure to the UVR
emitted by the GMAW of mild steel is quite hazardous. It is thought that workers are often
exposed to UVR when the arc is started1). Although the exposure is brief for each start of an
arc, this may occur often because workers usually start an arc many times in a day. Therefore,
the actual total exposure time may easily exceed the allowable daily exposure times
determined in this study. Thus, it was concluded that if workers engage in the GMAW of
mild steel without adequate protection, they are exposed to hazardous quantities of UVR
Chapter IV
Hazard of Ultraviolet Radiation Emitted in Gas Metal Arc Welding of Mild Steel
82
for short periods of time.
One of the authors previously measured the UVR emitted during the GMAW of mild
steel when using 100% CO2 as a shielding gas 9) and obtained an effective irradiance of
0.028–0.785 mW/cm2 at a distance of 1 m for welding currents of 120–500 A. Assuming
that the effective irradiance decreases as the inverse square distance from the arc, the
effective irradiance would be 0.106–3.14 mW/cm2 at 0.5 m from the arc, which is roughly
half the effective irradiance obtained in the present study for the same type of welding. This
difference is considered to be because of differences in welding conditions such as the
welding device, welding wire, and ventilation conditions.
In this study, no local exhaust ventilation system was used during the measurement
of UVR because local exhaust ventilation is usually not used in the welding workplace.
Local exhaust ventilation removes the welding fume, which strongly mitigates UVR by
scatter and absorption. Therefore, if local exhaust ventilation had been used during the
measurement, the effective irradiance would have been higher.
Assuming that the effective irradiance of UVR decreases as the inverse square
distance from the arc, the allowable daily exposure times at a distance of 5 m from the arc
will be in the range of 23–590 s. Thus, even at a distance of 5 m from the arc, exposure to
UVR is hazardous in cases in which the emitted UVR is intense. Moreover, even in cases in
which the emitted UVR is weak, I sure that prolonged exposure is hazardous. Thus, in cases
where the GMAW of mild steel is performed, it is necessary to take precautions to ensure
that surrounding workers are not exposed to the UVR emitted by the arc.
4.4.1 Influence of the type of shielding gas and the welding current
The effective irradiance measured in this study, regardless of the pulsed current and the type
of shielding gas, increased with increasing welding current (Figures 4.2 and 4.3). This trend
Chapter IV
Hazard of Ultraviolet Radiation Emitted in Gas Metal Arc Welding of Mild Steel
83
was also previously observed for the GMAW of mild steel using 100% CO29) and 5% O2 +
95% Ar6) as the shield gas. More recently, similar trend was also observed the GMAW and
the GTAW of aluminum14,15) and magnesium alloys16). Thus, the welding current is an
important factor influencing the degree of hazard of the UVR emitted during the welding
process; the UVR hazard can be understood to be a rapidly increasing function of the
welding current.
The effective irradiance of the UVR generated during steady 80% Ar + 20% CO2
welding was in the range of 0.51–12.9 mW/cm2 and increased with increasing welding
current. In particular, a significant difference in the increase in effective irradiance for
welding currents from 100 to 250 A and from 250 A upward was observed. In the arc
welding, the shape of the electrode tip has a strong influence on the stability of the arc. In
GMAW, since the welding wire of the consumable electrode is used for the electrode, the
shape of the tip of the electrode always changes, and the shape of the wire tip greatly differs
depending on the transfer form of the droplet. Therefore, the vicinity of the arc during
welding was observed. As shown in Figure 4.4, short-circuit transfer was observed at 100
A. In short-circuit transfer, the tip of the welding wire melted by the heat of arc is short-
circuited with the base metal, and is shifted to the base metal17). In addition, globular transfer
was observed at 250 A. In globular transfer, the welding wire tip melted by the arc and
grown to large drops lager than wire diameter is transferred to the base metal17). As also
shown in Figure 4.4, it was not possible at 300 A to observe the droplets, which were blocked
by the welding arc. However, the wire tip was pointed, and because no change appeared in
the shape of the wire tip with the passage of time, I assumed this was spray transfer. In spray
transfer, the welding wire tip melted by the arc is transferred to the base material with a
grain smaller than the wire diameter17). These results were consistent with the research of
Takeuchi et al.18). The effective irradiance of the UVR emitted by steady 80% Ar + 20%
Chapter IV
Hazard of Ultraviolet Radiation Emitted in Gas Metal Arc Welding of Mild Steel
84
CO2 welding increased with increasing welding current from 100 to 250 A, and no change
was seen in this increasing trend (Figure 4.2). Therefore, the effect of changing the metal
transfer mode from short-circuiting to globular on the effective irradiance was considered
to be small. However, the effective irradiance increased rapidly between 250 A and 300 A.
The metal transfer mode changed to spray transfer from globular transfer. The amount of
metal vapor in the arc during spray transfer is large compared to that during globular
transfer19), and the properties of light emitted by the arc welding are affected by the amount
of metal vapor blending into the arc20). Therefore, the cause of the rapid increase in the
effective irradiance from 250 to 300 A is considered to be because of the change in the metal
transfer mode (globular transfer to spray transfer).
The effective irradiance of the UVR emitted during 100% CO2 welding was in the
range of 0.69–7.4 mW/cm2 and increased with increasing welding current. Takeuchi et al.
reported that for 100% CO2 welding, the transition from short-circuit transfer to globular
transfer takes place at approximately 250 A18). However, in the present study, no clear
difference was seen in the effective irradiance vs. current trend between short-circuit
transfer and globular transfer. The effective irradiance was approximately the same for
steady 80% Ar + 20% CO2 welding and 100% CO2 welding at 250 A or less. However, a
significant difference was observed at 300 A or higher. By observation of the arc during
welding, the metal transfer mode of steady 80% Ar + 20% CO2 welding was spray transfer
and that of 100% CO2 welding was globular transfer. Therefore, the effective irradiance is
considered to depend on the metal transfer mode because of the differences in the shielding
gas composition between them, and the effective irradiance increases with the transition to
spray transfer. As shown above, the UVR emitted during the GMAW of mild steel was very
hazardous during spray transfer. The welding operator must recognize that welding under
spray transfer conditions is extremely dangerous, so it is necessary to take adequate
Chapter IV
Hazard of Ultraviolet Radiation Emitted in Gas Metal Arc Welding of Mild Steel
85
protective measures.
(a) Short-circuiting transfer.(The effective irradiance is 0.51 mW/cm2.)
(b) Globular transfer. (The effective irradiance is 2.7 mW/cm2.)
(c) Spray transfer. (The effective irradiance is 8.9 mW/cm2.)
Fig. 4.4. The metal transfer at no-pulsed 80%Ar+20%CO2 welding
4.4.2 The influence of pulsed current on the UVR hazard
The effects of pulsed current on the degree of the UVR hazard was examined. As shown in
Figure 4.3, the effective irradiance of the UVR emitted during pulsed 80% Ar + 20% CO2
1.0 mm Welding current 100 A
1.0 mm Welding current 250 A
Welding current 300 A 1.0 mm
Chapter IV
Hazard of Ultraviolet Radiation Emitted in Gas Metal Arc Welding of Mild Steel
86
welding increased with increasing current and was 3.0–6.7 times larger compared with that
emitted during steady 80% Ar + 20% CO2 welding at each welding current. The effective
irradiance was observed in the vicinity of the arc and the metal transfer mode was spray
transfer for the entire current range. Example photographs of the welding under these
conditions are shown in Figure 4.5.
Fig. 4.5 The metal transfer at pulsed 80%Ar+20%CO2 welding (spray transfer). (The
effective irradiance is 3.4 mW/cm2.)
For steady 80% Ar + 20% CO2 welding, the short-circuit or globular transfer modes
were observed at 250 A or less (Figure 4.4). The amount of metal vapor in the arc during
spray transfer is large compared to that during short-circuit and globular transfer19). In
addition, the properties of the light emitted during the arc welding are affected by the amount
of metal vapor blended into the arc20). Therefore, I sure that the effective irradiance of the
UVR generated by spray transfer for a pulsed current is very large compared with that
produced by the short-circuit and the globular transfer modes for a steady welding current.
These results confirm that the effective irradiance is strongly influenced by the pulsed
current, and the degree of the effect increases with decreasing pulsed current. In recent years,
the demand for mild steel thin plate welding has increased to reduce the weight of equipment
that needs to be transported. For thin plate welding, low welding current of less than 100 A
1.0 mm Welding current 100 A
Droplet Droplet Droplet
Chapter IV
Hazard of Ultraviolet Radiation Emitted in Gas Metal Arc Welding of Mild Steel
87
was used. In addition, a digital inverter-type pulsed arc welding machine was used to
increase the working efficiency.
In this study, the effective irradiance of the UVR that occurred during pulsed 80% Ar
+ 20% CO2 welding at 100 A was 1.2 times greater than the effective irradiance during
steady 80% Ar + 20% CO2 welding at 250 A. Therefore, welding operators need to
recognize the very high hazard of the UVR when they are welding with pulsed current, and
supervisors must take adequate protection measures for the peripheral workers who are not
welding.
4.5 Conclusions
GMAW of mild steel leads to the emission of intense UVR. The exposure to this
radiation is considered hazardous according to the ACGIH guidelines. This UVR hazard
exhibits the following characteristics. (1) It is more hazardous at higher welding currents
than at lower welding currents. (2) At higher welding currents, it is more hazardous when
80% Ar + 20% CO2 is used as a shielding gas than when 100% CO2 is used. (3) It is more
hazardous for pulsed welding currents than for steady welding currents. (4) It appears to
depend on the metal transfer; the hazard of the UVR emitted during spray transfer is the
highest.
4.6 References
1) The Japan Welding Engineering Society, 1980. Shakouhogogu no seinouhyouka tou ni
kansuru chousa kenkyu seika houkokusyo, A research report on the performance of eye
protectors against optical radiation, The Japan Welding Engineering Society. (in
Japanese)
Chapter IV
Hazard of Ultraviolet Radiation Emitted in Gas Metal Arc Welding of Mild Steel
88
2) Japan Standards Association, 2007. The Japan Society for Analytical Chemistry,
Technical terms for analytical chemistry: optical part, JIS K0212, Japan Safety
Appliances Association.
3) International Commission on Illumination, 2011. International lighting vocabulary,
2011, CIE Standard CIE S 017/E: 2011, Vienna, International Commission on
Illumination.
4) Sliney DH, Wolbarsht M, 1980. Safety with Lasers and Other Optical Sources, New
York, Plenum press.
5) Lyon TL, Marshall WJ, Sliney DH, Krial NP, Del Valle PF, 1976. Nonionizing radiation
protection special study No. 42-0053-77, Evaluation of the potential from actinic
ultraviolet radiation generated by electric welding and cutting arcs, Maryland, US Army
Environmental Hygiene Agency Aberdeen Proving Ground ADA033768.
6) World Health Organization Office of Global and Integrated Environmental Health, 1995.
Health and environmental effects of ultraviolet radiation: a summary of Environmental
health criteria 160: ultraviolet radiation, Geneva, World Health Organization.
7) Emmet EA, Buncher CR, Suskind RB, Rowe KW, 1981. Skin and eye diseases among
arc welders and those exposed to welding operations, Journal of Occupational Medicine
23: 85–90.
8) Okuno T, Saito H, Hojo M, Kohyama N, 2005. Hazard evaluation of ultraviolet radiation
emitted by arc welding and other processes, Occupational Health Journal 28(6): 65-71.
(in Japanese)
9) Okuno T, Ojima J, Saito, H, 2001. Ultraviolet radiation emitted by CO2 arc welding,
The Annals of Occupational Hygiene 45(7): 597–601.
Chapter IV
Hazard of Ultraviolet Radiation Emitted in Gas Metal Arc Welding of Mild Steel
89
10) Okuno T, Saito H, Hojo M, Kohyama N, 2005. Hazard evaluation of ultraviolet radiation
emitted by arc welding and other processes, Occupational Health Journal 28(6): 65-71.
(in Japanese)
11) Gigahertz-Optik, 2014. X13 Manual version 12: 14.
12) Japanese Industrial Standards Committee, 2010. Rolled steels for general structure, JIS
G 3101, Japan Standards Association. (in Japanese).
13) Japanese Industrial Standards Committee, 2009. Aluminum and aluminum alloy
welding rods and wires, JIS Z 3232, Japan Standards Association. (in Japanese)
14) Nakashima H, Utsunomiya A, Fujii N, Okuno T, 2014. Study of ultraviolet radiation
emitted by MIG welding of aluminum alloys, Journal of light metal welding 52(8): 290-
298. (in Japanese)
15) Nakashima H, Utsunomiya A, Fujii N, Okuno T, 2016. Hazard of ultraviolet radiation
emitted in gas tungsten arc welding of aluminum alloys, Industrial Health 54(2): 149–
159.
16) Nakashima H, Fujii N, Okuno T, Enomoto M, 2016. Hazard of ultraviolet radiation
emitted in tungsten inert gas and metal inert gas welding of magnesium alloys, Journal
of Light Metal Welding 54(1): 17–23. (in Japanese).
17) Japanese Industrial Standards Committee, 2013. Welding and allied processes–
Vocabulary–Part 2, Welding process, JIS Z 3001-2, Japan Standards Association. (in
Japanese).
18) Takeuchi Y, Horota A, 1980. Influence of gas composition of metal active gas arc
welding on operative weldability and mechanical properties of weld metal, Electric
Furnace Steel 52(1): 34–42. (in Japanese)
19) Ogino Y, Hirata Y, 2015. Numerical simulation of GMA metal transfer phenomena
including arc plasma, Quarterly Journal of the Japan Welding Society 33(1): 1–12. (in
Japanese).
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Hazard of Ultraviolet Radiation Emitted in Gas Metal Arc Welding of Mild Steel
90
20) Tsujimura T, Tanaka M, 2012. Numerical simulation of heat source property behavior
in GMA welding, Quarterly Journal of the Japan Welding Society 30(1): 68–76. (in
Japanese).
Chapter V
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding and Gas Metal Arc Welding of Magnesium Alloys
91
Chapter V
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding
and Gas Metal Arc Welding of Magnesium Alloys
Abstract
Ultraviolet radiation (UVR) emitted during arc welding frequently causes acute health
effects such as keratoconjunctivitis and erythema. The hazard of UVR varies depending on
the welding method and the welding conditions. For this reason, it is important to identify
the levels of UVR that are present under various conditions. In the present study, evaluated
the hazard of UVR emitted during gas tungsten arc welding (GTAW) and gas metal arc
welding (GMAW) of magnesium alloys were experimentally according to the American
Conference of Governmental Industrial Hygienists (ACGIH) guidelines. The distance
between the arc and the UVR detector was 500 mm.
The effective irradiances measured in the present study are in the range of 0.85 to 8.9
mW/cm2. The maximum allowable exposure times corresponding to these levels are 0.3 to
3.5 s/day, which are extremely small values for daily accumulated exposure times.
This demonstrates that, in practice, exposure to UVR emitted by GTAW and GMAW of
magnesium alloys are quite hazardous. In addition, I found the following properties of the
hazard of UVR. (1) The hazard of UVR generated during welding of magnesium alloys is
higher for GMAW than for GTAW. (2) The hazard of UVR is higher at higher welding
currents. (3) The hazard increases in GTAW when the shielding gas contains helium.
Keywords: ultraviolet radiation, effective irradiance, exposure time, gas metal arc welding,
gas tungsten arc welding, magnesium alloys
Chapter V
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding and Gas Metal Arc Welding of Magnesium Alloys
92
5.1 Introduction
Magnesium alloys are promising as structural materials because of their excellent specific
strength and vibration damping properties. However, their flammability and difficulty in
plastic forming have limited the application of these alloys. Nevertheless, with the
development of a flame-retardant magnesium alloy and the establishment of manufacturing
technology for the expanded use of magnesium alloys, the application of this alloy to
structures in various fields is expected1,2). Moreover, with the development of a welding
wire made of flame-retardant magnesium alloy, welding of magnesium alloys is expected
in the future3).
As in the case of arc welding of steel or aluminum alloys, UVR is emitted in the arc
welding of magnesium alloys. Previous studies by the present authors4,5) have clarified that
the hazard of UVR emitted during GMAW of aluminum alloys is strongly influenced by
magnesium contained in the base metal and the welding wire. Based on these considerations,
I assume that the hazard of UVR generated during arc welding of magnesium alloys is high.
Ultraviolet radiation causes acute health effects, such as inflammation of the conjunctiva
and the cornea as well as erythema (sunburn), and accounts for delayed health effects, such
as cataracts and skin cancer6). In particular, numerous incidences of keratoconjunctivitis and
erythema have been reported at actual welding sites7,8). As a basis for protective measures
for workers, it is desirable to obtain a quantitatively evaluation of the hazard of UVR.
However, there has been no report on the hazard of UVR emitted during the welding of
magnesium alloys. As such, in the present study, the UVR emitted during GTAW and pulsed
gas metal arc welding (GMAW-P) of magnesium alloys was measured as a basic for
developing preventive measures against the adverse health effects of UVR emitted during
arc welding of magnesium alloys. In the present study, the effects of welding method,
welding current, and shielding gas on the hazard of UVR are quantitatively evaluated
Chapter V
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding and Gas Metal Arc Welding of Magnesium Alloys
93
according to the recommendations of the American Conference of Governmental Industrial
Hygienists (ACGIH)9), the International Commission on Non-Ionizing Radiation Protection
(ICNIRP)10), and the Japanese Industrial Standard (JIS) Z 8812 (Hazardous Irradiation
Measurement Method)11).
5.2 Hazard assessment of UVR
The ACGIH defined threshold limit values (TLVs) as guidelines for exposure levels that
will prevent adverse health effects in almost all healthy workers, even under daily exposure.
Among these, since the hazard of UVR to the human body varies with wavelength, TLVs of
UVR in the wavelength range of 180 nm to 400 nm, excluding ultraviolet lasers, have been
determined. The TLV of UVR has a maximum value of 3 mJ/cm2 for a wavelength of 270
nm, and the hazard for each wavelength is expressed as a function of that at 270 nm in terms
of relative spectral effectiveness.
According to the ACGIH guidelines, the hazard of UVR as a cause of acute health
effects is measured in terms of effective irradiance, which is defined as follows:
where Eeff is the effective irradiance (mW/cm2), Eλ is the spectral irradiance at wavelength
λ (mW/(cm2·nm)), S(λ) is the relative spectral effectiveness at wavelength λ, and Δλ is the
bandwidth (nm).
The TLV for 270 nm has been determined by the ACGIH to be 3 mJ/cm2. If UVR is
irradiated to the unprotected skin and eyes, in general, the maximum exposure time for a
broadband UV source can be determined as follows:
Chapter V
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding and Gas Metal Arc Welding of Magnesium Alloys
94
𝑡𝑚𝑎𝑥 =0.003 𝐽 𝑐𝑚2⁄
𝐸𝑒𝑓𝑓 ・・・・・(2)
where tmax is the maximum daily exposure time (s), and Eeff is the effective irradiance
(mW/cm2).
5.3 Methods
5.3.1 Outline of experimental welding
In the present study, the effective irradiance of UVR during GTAW and GMAW-P of
magnesium alloys were measured. For each welding method, the flat-position forehead
welding was performed using a torch inclination 110°. The torch for GTAW was fixed at a
distance of 4 mm between the tip of the electrode and the base metal, where the electrode
was 6 mm from the tip of the nozzle. Then, melt-run welding, in which only the base metal
is melted and no filler rod is used, was carried out at 100 to 200 A using alternating current.
In contrast, in GMAW-P, the torch was fixed at a distance of 20 mm between the tip of the
contact tip and the base metal, and bead-on-plate welding, in which the base metal is melted
with a welding wire, was performed at 100 to 170 A using a pulsed direct current (welding
wire +). A voltage corresponding to the welding current preset by the manufacturer was used
as the welding voltage. Table 5.1 lists the welding conditions.
Two types of base metals were used, AZ3112) and AZX611, and an AZX611 welding
wire. Table 5.2 lists the chemical compositions of the base metals and welding wire. In
GTAW, it is necessary to use a welding current appropriate for the thickness of the base
metal, but it is still difficult to purchase small quantities of non-combustible magnesium
alloy for testing purposes. Since AZ31 and AZX611 contain largely the same chemical
components, AZ31 with thicknesses of 3 mm and 10 mm were used to investigate the
influence of welding current in GTAW on the effective irradiance. All other experiments
used AZX611. The planar dimensions of the base metal in all cases were 200 mm × 50 mm,
Chapter V
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding and Gas Metal Arc Welding of Magnesium Alloys
95
regardless of the welding method. In the present study, in the measurement of the UVR, the
position of the welding torch was fixed so as to produce arcs in the same position, and the
base metal was fixed on a movable table, which was moved linearly for welding.
Table 5.1 Welding conditions
GTAW GMAW
Welding equipment DA300P DP350
Manufacturer DAIHEN Welding and Mechatronics Systems Co., Ltd.
Welding current (A) 100, 150 200 100, 120, 150, 170
Welding speed (mm/min) 200 300
Size of base metal (mm) t3 × 200 × 50 t10 × 200 × 50 t10 × 200 × 50
Electrode (wire) diameter (mm) 3.2 (1.2)
Inner diameter of nozzle (mm) 12.7 17.1
Shielding gas 100% Ar or 50% Ar + 50% He
Shielding gas flow rate (l/min) 15 20
Table 5.2 Chemical compositions of base metals and welding wire (mass%)
Alloy
Size (mm) Mg Al Zn Mn Fe Si Ca
Base metal
AZ31 t3 × 200 × 50 Balance 2.90 0.87 0.28 0.00 0.02 -
t10 × 200 × 50 Balance 2.93 1.01 0.45 0.00 0.01 -
AZX611 t10 × 200 × 50 Balance 5.90 0.60 0.30 0.00 0.02 1.04
Welding wire AZX611 1.2 Balance 5.90 0.60 0.22 0.00 0.03 1.00
5.3.2 Measured effective irradiance of UVR
For the UVR measurements, an X13 hazard light meter and an XD-45-HUV UV-hazard
detector head (both from Gigahertz-Optik) were used, which were designed for measuring
effective irradiance. The detector head has three sensors. The measurement of the effective
Chapter V
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96
irradiance used two sensors UV-CB (measurement wavelength range: 200 to 320 nm) and
UV-A (measurement wavelength range: 320 to 400 nm). Table 3.1 lists the characteristics
of these sensors. The relative spectral responsivity of the detector head was adjusted to
coincide with the relative spectral effectiveness as documented by the manufacturer. Figure
2.1 shows the relationship between the relative spectral effectiveness and the relative
spectral responsivity of the detector head13). The relative spectral responsivity of the detector
head agreed well with the relative spectral effectiveness at around 270 nm. However, since
the relative spectral responsivity of the detector head is unknown in the wavelength range
of approximately 225 nm or less, some discrepancy between the relative spectral
responsivity and the relative spectral effectiveness is observed from 310 to 320 nm.
However, the effective irradiance of a light source that contains UVR of various
wavelengths, such as welding arc emitted by arc welding, is less influenced by the difference
between the relative spectral effectiveness and the relative spectral responsivity of the
detector head. In the present study, the spectral irradiance at wavelengths of 200 to 400 nm
was measured. For each calculated value, the effective irradiance was obtained using
equation (1) and the detector responsivity. The difference between the respective values was
approximately 4%, and that obtained based on the detector responsivity was larger. In
addition, although the detector responsivity in the wavelength range of 180 to 200 nm is
unknown, in the product of the relative spectral effectiveness and the bandwidth of the
wavelength, the ratio of the integrated value in the wavelength range from 180 to 200 nm
to the whole is approximately 2%. Thus, it was concluded that this detector head is well
suited to measure the effective irradiance. In actual experiments, the value measured by the
measurement devices is the effective radiant exposure (J/m2). Dividing this value by the
measurement time yields the effective irradiance. The measurement device was calibrated
by the manufacturer and was used within the one year of calibration.
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97
The position of the welding torch was fixed to produce arcs in the same position, and
the base metal was fixed on a movable table. The distance between the arc and the detector
head was set to 500 mm in order to mimic the actual distances to welders. The angles of the
detector head from the surface of the base metal were 40° for GTAW and were 50° for
GMAW. These angles were observed in previous studies to provide the maximum effective
irradiance for each welding method for aluminum alloys4,14). In addition, the angle of the
detector head from the welding direction was 90° for both welding methods. Figure 5.1
shows a schematic diagram of the experimental setup for measuring effective irradiance.
The measurement times were set to 40 s for GTAW and 20 s for GMAW. Measurements
were repeated five times for each set of conditions and then averaged. In order to exclude
the time required for the arc to stabilize immediately after welding begins and the time
required for the movable table to accelerate, measurements did not begin until 5 s after the
start of welding.
Figure 5.1 Experimental setup for measuring effective irradiance and spectral irradiance.
Chapter V
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding and Gas Metal Arc Welding of Magnesium Alloys
98
In the present study, no local exhaust ventilation system was used during the
measurement of UVR because local exhaust ventilation is usually not used in welding
workplaces (local exhaust ventilation may disturb the airflow around the arc and cause
welding defects).
5.3.3 Influence of the magnitude of the welding current
In order to investigate the influence of welding current, the effective irradiances of GTAW
and GTAW-P were measured.
For GTAW, the effective irradiance was measured for the welding current range of 100
to 200 A. The base metal used was AZ31 of 3 mm in thickness at 100 and 150 A and 10 mm
in thickness at 200A.
For GTAW-P, the base metal and welding wire used were AZX611. The thickness of
the base metal was 10 mm. Regarding the range of welding current, in this experiment,
welding wire with a diameter of 1.2 mm could not be applied with a welding current
exceeding 170 A, so the welding current range was 100 to 170 A. Regarding the shielding
gas, 100% Ar was used for each welding method. Moreover, AZX 611 was used as the base
metal under all conditions (external dimensions: t10 × 200 × 50 mm).
5.3.4 Impact of the type of electrode and the shielding gas components
In order to investigate the influence of the electrode type, the effective irradiances during
GTAW were measured using a pure tungsten electrode (YWP)15) and a 2%-cerium-oxide-
containing electrode (YWCe-2)15), both of which are commonly used in GTAW. The
electrode diameter was 3.2 mm, and the welding current was 200 A. Moreover, AZX 611
was used as the base metal under all conditions (external dimensions: t10 × 200 × 50 mm).
In order to investigate the influence of the type of shielding gas, I conducted GTAW
Chapter V
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding and Gas Metal Arc Welding of Magnesium Alloys
99
and GMAW-P and measured the resulting UVR when using 100% Ar and 50% He + 50%
Ar. The welding current was 200 A for GTAW. Moreover, for GMAW-P, a welding current
of 165 A or higher could not be applied when using 50% Ar + 50% He. Therefore, in
GMAW-P, the effective irradiance was measured at 150 A, at which the welding current
stabilized.
For such broadband UVR of the arc, by analyzing the intensity of irradiance of each
wavelength, factors that affect the hazard of UVR can be specified. In addition, GMAW-P
is more likely to exhibit light emission than GTAW. This is because the amount of
penetration into the arc plasma of a metal element or the like, which causes the emission of
UVR, is large in GMAW-P16). Therefore, the spectral irradiance of UVR for the cases of
using 100% Ar and 50% Ar + 50% He in GMAW-P were measured at a welding current of
150 A. Here, the spectral irradiance is defined with respect to the plane irradiated with light
and represents the unit wavelength of light irradiated within the unit area and the energy per
unit time (unit: W/cm2∙nm). The measurement apparatus was a multichannel spectrometer
(HSU-100S, Asahi Spectra Co., Ltd.). The measurement wavelength range of the apparatus
was 200 to 1,000 nm, and the wavelength precision of the apparatus was ±1.2 nm. The
detector was positioned at an angle of 5° from the surface of the base metal and at an angle
of 90° from the welding direction. The distance from the arc was set to 2,500 mm. The
measurement time was automatically adjusted by the apparatus according to the intensity of
the light. Figure 5.1 shows the experimental setup for measuring effective irradiance and
spectral irradiance.
5.4 Results
Figures 5.3 and 5.4 show the effective irradiance for various welding conditions. The
effective irradiance measured in the present study at a distance of 500 mm from the arc was
Chapter V
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding and Gas Metal Arc Welding of Magnesium Alloys
100
in the range of 0.80 to 8.9 mW/cm2 for GTAW and 4.6 to 7.8 mW/cm2 for GMAW-P. The
allowable daily exposure times corresponding to these values are 0.33 to 3.8 s for GTAW
and 0.30 to 0.65 s for GMAW-P.
As shown in Figure 5.2, in GTAW of the magnesium alloy, the effective irradiance
increased as the welding current increased. For GMAW-P, although the data fluctuation was
large, the effective irradiance increased roughly as the welding current increased. For the
same welding current, the effective irradiance of GMAW-P was 1.5 to 5.8 times higher than
that of GTAW.
As shown in Figure 5.3, in GTAW, the effective irradiance when YWCe-2 was used
for the electrode was approximately 20% higher than that when YWP was used for the
electrode. Moreover, the effective irradiance when 50% Ar + 50% He was used as the
shielding gas was approximately twice that when using 100% Ar as the shielding gas. For
GMAW-P, the effective irradiance using 50% Ar + 50% He was approximately 25% lower
than that when using 100% Ar.
Figure 5.2 Effective irradiance for different welding methods and welding currents.
Chapter V
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding and Gas Metal Arc Welding of Magnesium Alloys
101
Figure 5.3 Effective irradiance for different electrodes and shielding gases.
5.5 Discussion
The effective irradiance measured in the present study at a distance of 500 mm from the arc
was in the range of 0.80 to 8.9 mW/cm2 for GTAW and in the range of 4.6 to 7.8 mW/cm2
for GMAW-P. The allowable daily exposure times corresponding to these values are 0.33 to
3.8 s for GTAW and 0.30 to 0.65 s for GMAW-P. These results indicate that exposure to the
UVR emitted by GTAW and GMAW-P of magnesium alloys is quite hazardous. It is thought
that workers are often exposed to UVR when the arc is started7). Although the exposure is
brief for each start of an arc, this may occur often because workers usually start an arc
several times a day. Therefore, the actual total exposure time may easily exceed the
allowable daily exposure times determined in the present study. Thus, it was concluded that
if workers engage in GTAW and GMAW-P of magnesium alloys without adequate
protection, they will be exposed to hazardous levels of UVR for short periods of time.
Assuming that the effective irradiance of UVR decreases as the inverse square of
the distance from the arc, then the allowable daily exposure time at a distance of 5 m from
Chapter V
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding and Gas Metal Arc Welding of Magnesium Alloys
102
the arc will be in the range of 33 to 380 s for GTAW and in the range of 30 to 65 s for
GMAW-P. Thus, even at a distance of 5 m from the arc, exposure to UVR is hazardous in
cases in which the emitted UVR is intense. Moreover, even in cases in which the emitted
UVR is weak, I sure that prolonged exposure is hazardous. Thus, for cases in which GTAW
and GMAW-P of magnesium alloys is performed, it is necessary to take precautionary
measures so that surrounding workers will not be exposed to UVR emitted by arcs.
5.5.1 Influence of the magnitude of welding current on the hazard of UVR
The effective irradiance measured during both GTAW and GMAW-P increases with the
increase in welding current (Figure 5.1). Therefore, the effective irradiance during GTAW
and GMAW-P of magnesium alloys was strongly influenced by the welding current. This
trend was similarly observed in previous studies involving other metals4,5,14,17-21). Thus,
welding current is an important factor influencing the hazard of UVR emitted during the
welding process. In other words, the UVR hazard can be understood to be a rapidly
increasing function of the welding current.
At 200 A, the effective irradiance of GTAW was approximately 7.4 times that at 100
A, and, at 170 A, the effective irradiance of GMAW-P was approximately 1.7 times that 100
A. Therefore, the hazard of UVR for GTAW is more sensitive to welding current, as
compared to GMAW-P. This is believed to be due to the UVR being absorbed and scattered
by fumes generated during GMAW-P. The amount of fumes generated during GMAW-P was
larger than that generated during GTAW, and the amount of fumes increased with the
welding current. Since UVR is strongly absorbed and scattered by fumes as the welding
current increases, it is inferred that the dependence of the effective irradiance on welding
current is reduced in GMAW-P.
Chapter V
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding and Gas Metal Arc Welding of Magnesium Alloys
103
5.5.2 Influence of the type of electrode and the components of the shielding gas
The effective irradiance when YWCe-2 was used was higher than that when YWP was used
as the electrode in GTAW. Compared to YWP, for the case in which YWCe-2 was used as
the electrode in GTAW, less melt deformation was observed at the electrode tip and better
arc convergence was also observed22). It is thought that the temperature of the molten pool
and its surroundings increased due to the high convergence of the arc. Consequently, the
amount of metal vapor increased, and the effective irradiance increased.
The UVR emitted by GTAW using 50% Ar + 50% He is more hazardous than that
when using 100% Ar, and the effective irradiance when using 50% Ar + 50% He was
measured to be approximately twice that when using 100% Ar. A cross section of the weld
is shown in Figure 5.4. In this case, 50% Ar + 50% He was used as the shielding gas, and
increases in the melting width and penetration depth were observed, as compared to the case
in which 100% Ar was used. Therefore, one reason the effective irradiance became high
may be that the shielding gas contained He, thereby expanding the molten pool and
increasing the amount of metal vapor from the molten pool surface.
100% Ar 50% Ar + 50% He
Figure 5.4 Effect of shielding gas on penetration depth.
For GMAW-P, the effective irradiance of UVR emitted when using 50% Ar + 50%
He was lower than that when using 100% Ar. This trend is different from that for GTAW.
Therefore, GMAW-P was performed using 100% Ar and 50% Ar + 50% He, and the spectral
5 mm 5 mm
Chapter V
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding and Gas Metal Arc Welding of Magnesium Alloys
104
irradiances of the arcs during welding were measured. Figure 5.5 shows the relationship
between spectral irradiance for different shielding gases and relative spectral effectiveness
for GMAW-P. A strong emission from magnesium was observed in the vicinity of 280 nm,
where the hazard of UVR is high. Emissions caused by calcium and zinc contained in the
base material and the welding wire were predicted, but could not be confirmed. In addition,
a similar spectral profile was observed regardless of the shielding gas, and clear emissions
from argon and helium were not confirmed.
Figure 5.6 shows the scattering situation for welding fumes during GMAW-P. The
amount of welding fumes generated when 50% Ar + 50% He was used as the shielding gas
was larger than when 100% Ar was used, and it was observed that the duct installed above
the welding torch could not completely collect dust. Since the main components of the
welding wire have boiling points of 1,760 K (calcium), 1,176 K (zinc), 2,759 K (aluminum),
and 1,370 K (magnesium), it was thought that these components were mixed in welding
fumes. Therefore, fumes generated in GMAW-P were collected and qualitatively analyzed
by a scanning electron microscope. Figure 5.7 shows the results of qualitative analysis of
the collected welding fumes. Since magnesium and oxygen were detected by the qualitative
analysis, the main component contained in welding fumes is likely to be magnesium oxide.
Moreover, calcium and zinc were not detected. Therefore, in GMAW-P, the reason why the
effective irradiance was lower when using 50% Ar + 50% He as the shielding gas is
presumed to be as follows. If helium is contained in the shielding gas, the wire tip
temperature and the arc column temperature increase, and the magnesium vapor amount
increases, which in turn increases UVR. At the same time, however, the amount of welding
fumes increases, because the amount of magnesium released outside the arc increases. The
scattered fumes envelop the arc, blocking UVR, which is then not detected by detectors.
Therefore, the effective irradiance of the UVR emitted when 50% Ar + 50% He is used as
Chapter V
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding and Gas Metal Arc Welding of Magnesium Alloys
105
the shielding gas in GMAW-P is thought to be low.
Figure 5.5 Relationship between spectral irradiance for different shielding gases and
relative spectral effectiveness for GMAW-P.
100% Ar 50% Ar + 50% He
Figure. 5.6 Scattering situation of the welding fumes.
Figure 5.8 shows the appearance of the collected fumes. A large number of
secondary particles having diameters of 0.03 to 0.05 μm that formed a chain were observed,
and fumes having particles of 0.1 to 0.3 μm in diameter were also observed. The relationship
Chapter V
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding and Gas Metal Arc Welding of Magnesium Alloys
106
between fume particle size and pneumoconiosis has been well documented, and particles of
0.1 μm to several micrometers in diameter, which can enter the lungs through respiration
and become deposited on the alveoli, have various effects on the lungs23). According to JIS
T 8151 (regarding dust masks)24), type-RS3 and -DS3 masks can collect 99.9% or more of
dust particles and so can be expected to reduce the influence of fumes on the human body.
Figure 5.7 Qualitative analysis of welding fumes by scanning electron microscope.
Figure 5.8 Appearance of the collected welding fumes.
Energy (keV)
1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0
O
Mg
Al
Inte
nsi
ty (
cps)
0.1μm
Chapter V
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding and Gas Metal Arc Welding of Magnesium Alloys
107
5.6 Conclusions
The GTAW and GMAW-P of magnesium alloys leads to the emission of intense UVR.
According to the ACGIH guidelines, exposure to this radiation is considered to be hazardous.
This UVR hazard exhibits the following characteristics. (1) The hazard of UVR generated
during welding is higher for GMAW-P than for GTAW. (2) The hazard of UVR is higher at
higher welding currents. In addition, GTAW is more susceptible to the welding current than
GMAW-P. (3) The hazard of UVR emitted during GTAW increases when the shielding gas
contains helium. (4) The hazard of UVR during the GTAW is increased by the use of cerium
oxide tungsten electrodes. (5) The UVR in GMAW-P is strongly affected by fumes
generated during welding, and the hazard is reduced by the increase in the amount of fumes.
5.7 References
1) Mori H, Fujino K, Kurita K, Chino Y, Saito N, Noda M, Komai H, Komai H, Obara H,
2013. Application of the flame-retardant magnesium alloy to high speed rail vehicles,
Materia Japan 10: 484-490. (in Japanese).
2) Katagiri H, Gonda Y, Sakurai Z, Hayakawa Y, 2014. J0410205 Mechanical properties
and press formability of twin-roll cast AZX611 magnesium alloy strip, Mechanical
Engineering Congress, Japan 2014. (in Japanese)
3) Ueda M, Takigawa Y, Kinomoto Y, Higashi K, 2015. MIG welding filler wire made of
flame retardant magnesium alloys, Alutopia 45: 21-27. (in Japanese).
4) Nakashima H, Utsunomiya A, Fujii N, Okuno T, 2014. Study of ultraviolet radiation
emitted by MIG welding of aluminum alloys, Journal of light metal welding 52(8): 290-
298. (in Japanese)
5) Okuno T, Kohyama N, Serita F, 2005. Ultraviolet radiation from MIG welding of
aluminum, Safety & Health Digest 51(9): 2-5. (in Japanese)
Chapter V
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding and Gas Metal Arc Welding of Magnesium Alloys
108
6) World Health Organization Office of Global and Integrated Environmental Health, 1995.
Health and environmental effects of ultraviolet radiation: a summary of Environmental
health criteria 160: ultraviolet radiation, Geneva, World Health Organization.
7) The Japan Welding Engineering Society, 1980. Shakouhogogu no seinouhyouka tou ni
kansuru chousa kenkyu seika houkokusyo, A research report on the performance of eye
protectors against optical radiation, The Japan Welding Engineering Society. (in
Japanese)
8) Emmet EA, Buncher CR, Suskind RB, Rowe KW, 1981. Skin and eye diseases among
arc welders and those exposed to welding operations, Journal of Occupational Medicine
23: 85–90.
9) The American Conference of Governmental Industrial Hygienists, 2015. 2015
Threshold limit values for chemical substances and physical agents and biological
exposures indices, Cincinnati, American Conference of Governmental Industrial
Hygienists.
10) International Commission on Non-Ionizing Radiation Protection, 2004. Guidelines on
limits of exposure to ultraviolet radiation of wavelengths between 180 nm and 400 nm
(incoherent optical radiation), Health Physics 87(2): 171-186.
11) Japanese Industrial Standards Committee, 1987. Measuring methods of eye-hazardous
ultraviolet radiation, JIS Z8812, Japan Standards Association. (in Japanese)
12) Japanese Industrial Standards Committee, 2011. Magnesium alloy sheets, plates, strips
and coiled sheets, JIS H4201, Japan Standards Association. (in Japanese).
13) Gigahertz-Optik, 2014. X13 Manual version 12: 14.
14) Nakashima H, Utsunomiya A, Fujii N, Okuno T, 2016. Hazard of ultraviolet radiation
emitted in gas tungsten arc welding of aluminum alloys, Industrial Health 54(2): 149–
159.
Chapter V
Hazard of Ultraviolet Radiation Emitted in Gas Tungsten Arc Welding and Gas Metal Arc Welding of Magnesium Alloys
109
15) Japanese Industrial Standards Committee, 2009. Aluminum and aluminum alloy
welding rods and wires, JIS Z 3232, Japan Standards Association. (in Japanese)
16) Tsujimura T, Tanaka M, 2012. Numerical simulation of heat source property behavior
in GMA welding, Quarterly Journal of the Japan Welding Society 30(1): 68–76. (in
Japanese).
17) Sliney DH, Wolbarsht M, 1980. Safety with Lasers and Other Optical Sources, New
York, Plenum press.
18) Lyon TL, Marshall WJ, Sliney DH, Krial NP, Del Valle PF, 1976. Nonionizing radiation
protection special study No. 42-0053-77, Evaluation of the potential from actinic
ultraviolet radiation generated by electric welding and cutting arcs, Maryland, US Army
Environmental Hygiene Agency Aberdeen Proving Ground ADA033768.
19) Okuno T, Saito H, Hojo M, Kohyama N, 2005. Hazard evaluation of ultraviolet radiation
emitted by arc welding and other processes, Occupational Health Journal 28(6): 65-71.
(in Japanese)
20) Okuno T, Ojima J, Saito, H, 2001. Ultraviolet radiation emitted by CO2 arc welding,
The Annals of Occupational Hygiene 45(7): 597–601.
21) Peng C, Lan C, Juang Y, Tsao T, Dai Y, Liu H, Chen C, 2007. Exposure assessment of
aluminum arc welding radiation, Health Physics 93(4): 298-306.
22) Matsuda F, Ushio M, Kumagai T, 1988. Comparative study on fundamental arc
characteristics with La-, Y-, Ce-Oxide tungsten electrodes, Quarterly Journal of the
Japan Welding Society 6(6): 199-204 (in Japanese).
23) The Japan Welding Engineering Society, Safety and Health and Environment committee,
2002. Yousetsu anzen eisei manyuaru, Tokyo, Sanpo Publications.
24) Japanese Industrial Standards Committee, 2005. Particulate respirators, JIS T8151,
Japan Standards Association. (in Japanese).
Chapter VI
Blue-light Hazard from Gas Metal Arc Welding of Aluminum Alloys
110
Chapter VI
Blue-light Hazard from Gas Metal Arc Welding of Aluminum Alloys
Abstract
The objective was to quantify the blue-light hazard from gas metal arc welding of aluminum
alloys. The exposure level is expected to depend on the welding conditions. Therefore, it is
important to identify the blue-light hazard under various welding conditions. Gas metal arc
welding of aluminum alloys was conducted under various welding conditions and the
spectral radiance of the arcs was measured. The effective blue-light radiance, which the
American Conference of Governmental Industrial Hygienists has defined to quantify the
exposure level of blue light, was calculated from the measured spectral radiance. The
maximum acceptable exposure duration per 10000 s for this effective blue-light radiance
was calculated.
The effective blue-light radiance measured in this study was in the range of 2.9–20.0
W/cm2·sr. The corresponding maximum acceptable exposure duration per 10000 s was only
5.0–34 s, so it is hazardous to view the welding arc. The effective blue-light radiance was
higher at higher welding currents than at lower welding currents, when pulsed welding
currents were used rather than steady welding currents, and when magnesium was included
in the welding materials. It is very hazardous to view the arcs in gas metal arc welding of
aluminum alloys. Welders and their helpers should use appropriate eye protection in arc-
welding operations. They should also avoid direct light exposure when starting an arc-
welding operation.
Keywords: aluminum; arc; blue light; effective radiance; gas metal arc welding; MIG
welding; photoretinopathy; welding
Chapter VI
Blue-light Hazard from Gas Metal Arc Welding of Aluminum Alloys
111
6.1 Introduction
It is well known that a welding arc emits ultraviolet radiation 1-7), which often causes
keratoconjunctivitis and skin erythema in workers8,9). A welding arc also emits intense
visible light. Extremely large numbers of workers are expected to be exposed to this visible
light by accidentally or mistakenly viewing welding arcs without adequate protection. These
workers include not only expert arc-welding professionals, whose numbers are estimated as
350,000 in Japan, but also workers who do not specialize in arc welding but perform it
occasionally, as well as workers engaged in other tasks in workplaces where other workers
are performing arc welding8).
Light-induced retinal injury has been reported in people who have stared at a welding
arc without adequate protection10-19). This injury appears as retinal changes such as edema
or a hole and is accompanied by symptoms such as decreased visual acuity, blurred vision,
or scotoma. These symptoms appear immediately or within a few hours after exposure and
then improve gradually over weeks or months. In some cases, patients completely recover,
whereas in other cases, patients still have symptoms several months after light exposure.
Thus, light-induced retinal injury associated with arc welding can be a severe disorder that
can have a significant impact on daily life.
The mechanism of light-induced retinal injury associated with arc welding is not
thermal because the temperature rise in the retina is estimated to be insufficient to cause a
burn; therefore, the injury mechanism is considered to be photochemical12). Photochemical
retinal injury, known as photoretinopathy, is caused by light primarily in the wavelength
region of 400–500 nm. Because the light in this region appears blue to the eye, it is called
blue light. Measures to prevent retinal injury due to arc welding are necessary. As the basis
for designing such measures, it is desirable to obtain a quantitative understanding of the
hazard of blue light emitted during arc welding. There are two sets of internationally
Chapter VI
Blue-light Hazard from Gas Metal Arc Welding of Aluminum Alloys
112
recognized guidelines for protection against blue light, the ACGIH guidelines20) and the
ICNIRP guidelines21) which are basically equivalent. In this study, blue light was evaluated
in accordance with the ACGIH guidelines.
Arc welding is performed with various metals. Arc welding of aluminum alloys is the
second most commonly used arc welding in workplaces after arc welding of mild steel.
Aluminum alloys exhibit excellent properties—light weight, high strength-to-weight ratio,
corrosion resistance, workability, and good appearance—and are widely used as raw
materials for structural products and components in a wide variety of fields, including
manufacture of railway vehicles, automobiles, ships, aerospace instruments, and chemical
instruments. The two primary welding methods for aluminum alloys are gas metal arc
welding (GMAW) and gas tungsten arc welding (GTAW). GMAW is a semi-automatic
process in which the wire is supplied automatically. In GMAW, an inert gas (argon, helium,
or a mixture of these gases) is used as a shielding gas. GMAW, which ensures good work
efficiency compared to GTAW, is used more widely in the workplace.
For a long time, GMAW was performed mostly by using steady current (GMAW-S).
However, because GMAW-S tends to be unstable at low welding currents, it is difficult to
weld thin plates of aluminum alloys with this welding method. Thus, GMAW-S is primarily
used for a plate thickness of 3 mm or more. In recent years, the welding power source of a
digital inverter type was developed. The digital inverter enables pulsed control of the
welding current. GMAW using the pulsed current (GMAW-P) is capable of stable welding
for a plate less than 3 mm in thickness. For this reason, GMAW-P is more widely used in
the workplace.
It is important to investigate the hazard of the blue light emitted in arc welding of
aluminum alloys under a wide range of conditions. A few studies have measured the blue
light in arc welding of aluminum alloys 22-24), and only two of these studies have determined
Chapter VI
Blue-light Hazard from Gas Metal Arc Welding of Aluminum Alloys
113
the effective blue-light radiance22,23). In these studies, the effective blue-light irradiance
(spectral irradiance weighted against the blue-light hazard function) was measured at a fixed
distance from the arc. The effective blue-light radiance was then calculated from the
effective blue-light irradiance by using the estimated size (area) of the arc. However, this
method provided inaccurate results, because the arc has no definite boundaries and
consequently no definite size. Thus, no reliable data on the effective blue-light radiance for
arc welding of aluminum alloys are available.
In the present work, the hazard of blue light emitted in GMAW of aluminum alloys
was quantitatively evaluated in accordance with the ACGIH guidelines (ACGIH, 2015). In
particular, I studied the impact of (i) the magnitude of welding current, (ii) the use of pulsed
welding current, (iii) the type of base metal and welding wire.
6.2 Methods
A welding arc emits visible light of various wavelengths. According to the ACGIH
guidelines (2015), the exposure level of visible light for causing retinal photochemical
injury is different depending on the light wavelength. For that reason, the hazard of visible
light is basically indicated by the effective blue-light radiance of a light source. The effective
blue-light radiance is defined by equation (1):
LB = ∑ Lλ・
700
305
B(λ)・∆λ ・・・・・(1)
In this equation, LB is the effective blue-light radiance of a light source, Lλ is the
spectral radiance of that light source, B(λ) is the blue-light hazard function and Δλ is the
wavelength band width. The blue-light hazard function indicates the degree of hazard at
Chapter VI
Blue-light Hazard from Gas Metal Arc Welding of Aluminum Alloys
114
each wavelength and has a maximum at wavelengths of 435 nm and 440 nm (Figure 6.1).
For the exposure durations (t) less than 10000 s (approximately 167 minutes or 2.8
hours), an acceptable exposure is expressed by equation (2):
LB ≦100 (J/cm2 ∙ sr)
t ・・・・・(2)
Alternatively, when LB exceeds 0.01 W/cm2·sr, the maximum acceptable exposure duration
per 10000 s tmax in seconds is calculated by equation (3)
tmax(s) =100
LB ・・・・・(3)
Figure 6.1 The blue-light hazard function (ACGIH, 2015). The blue-light hazard function
shows the effectiveness of light to produce photochemical retinal damage as a function of
wavelength.
To measure the spectral radiance, a spectroradiometer (SR-3AR, Topcon Technohouse
Chapter VI
Blue-light Hazard from Gas Metal Arc Welding of Aluminum Alloys
115
Corp.) was used. This spectroradiometer is capable of measuring the spectral radiance of a
light source averaged over its field of view.
Although spectral radiance in the wavelength range of 305–780 nm is required to
calculate effective blue-light radiance, as shown in equation (1), the shorter wavelength
range of 305–380 nm was ignored in the calculation in this study, because the
spectroradiometer can measure spectral radiance only in the wavelength range of 380–780
nm. This limitation can be justified because the blue-light hazard function has extremely
low values in this wavelength range (Figure 6.1) and therefore its contribution to effective
blue-light radiance is generally very small for broad-band light sources such as welding arcs.
In fact, calculations based on spectral distribution in the range of 200 nm to 1000 nm
measured for optical radiation emitted during GMAW of aluminum alloy5) show that the
contribution of the ultraviolet radiation region (300 nm to 380 nm) would be only
approximately 2%. The spectroradiometer was calibrated beforehand by the manufacturer
and was used within the one-year validity of that calibration. In order to decrease the light
intensity to a measurable level, the opening of the spectroradiometer was equipped with a
neutral density filter (400FN46-50S, Andover Corp.). After completion of the measurement,
the spectral radiance was corrected by the spectral transmittance of the neutral density filter
(400FN-46-50S, Andover Corp.), and the effective blue-light radiance and the maximum
acceptable exposure duration were calculated by equations (1) and (3), respectively.
The welding torch was fixed so that the arc remained in the same position, while the
base metal was placed horizontally on a travel device that was translated along a horizontal
line at a constant speed when the effective blue-light radiance was being measured. The
spectroradiometer was positioned at an angle of 45° from the surface of the base metal and
at an angle of 90° from the welding direction.
According to the ACGIH (2015), the diameter of the field of view for evaluation of
Chapter VI
Blue-light Hazard from Gas Metal Arc Welding of Aluminum Alloys
116
the blue-light hazard is 0.011 rad, which corresponds to a 3.3-mm-diameter circle at the
position of the arc for a welder whose eyes are assumed to be 300 mm from the arc. Thus,
the spectroradiometer was positioned so that its field of view would be a 3.3-mm-diameter
circle at the position of the arc. Figure 6.2 shows a schematic diagram of the experimental
setup for measuring the effective blue-light radiance. The integration time (exposure time)
was set in the range of 50–530 ms automatically by the spectroradiometer depending on the
light intensity. To exclude the time required to stabilize the arc and to accelerate the travel
device to a constant speed, measurement did not begin until 5 s after the start of welding.
Measurements were repeated five times for each set of conditions and the results were
averaged.
Figure 6.2 Experimental setup for measuring effective radiance (schematic diagram).
GMAW of aluminum alloys was performed in the experiments. The welding apparatus
used was a digital inverter-type pulsed arc welding machine (DP350, DAIHEN Welding and
Mechatronics Systems Co., Ltd.). The inclination of the welding torch was fixed at 110°.
The type of welding was bead-on-plate welding (simulated welding with no joint). Flat
position forehead welding was performed. The distance between the contact tip of the
welding torch and the base metal was 20 mm. The welding speed was 300 mm/min. Three
Chapter VI
Blue-light Hazard from Gas Metal Arc Welding of Aluminum Alloys
117
different types of base metals were used. The base metals were specified by the Japanese
Industrial Standards (JIS, 2014). The dimensions of the base material were 30 mm × 400
mm × 250 mm. Three different types of solid wires of diameter 1.2 mm were used. The
wires were also specified by JIS (2009). Table 1 presents the composition of these base
metals and the welding wires. The shielding gas was 100% Ar. The flow rate was 20 L/min.
6.2.1 Influence of the magnitude of the welding current and the use of pulsed current
To investigate the influence of the magnitude of the welding current and the use of pulsed
current, we measured the effective blue-light radiance of the arcs for GMAW-S and GMAW-
P. The base metal was A5083P-O (JIS, 2014) and the welding wire was A5183WY (JIS,
2009). The range of welding current was 100–250 A.
Table 6.1 Chemical composition of base metals and welding wires (mass%).
Base metal Si Fe Cu Mn Mg Cr Zn Ti Al
A1100P-H112 0.09 0.57 0.14 0 0 - 0.01 0.02 >99.00
A5083P-O 0.14 0.27 0.04 0.66 4.37 0.11 0.02 0.02 Balance
A6063BES-T5 0.44 0.19 0.03 0.02 0.5 0.02 0 0.02 Balance
Welding wire Si Fe Cu Mn Mg Cr Zn Ti Al
A1100WY MAX 0.95 (Si+Fe) 0.20 0.05 - - 0.10 -
>99.00 MIN - - 0.05 - - - - -
A4043WY MAX 6.00 0.80 0.30 0.05 0.05 - 0.10 0.20
Balance MIN 4.50 - - - - - - -
A5183WY MAX 0.40 0.40 0.10 1.00 5.20 0.25 0.25 0.15
Balance MIN - - - 0.50 4.30 0.05 - -
6.2.2 Influence of the type of base metal and the type of welding wire
To investigate the impact of the types of base metals and welding wires, the GMAW-P was
performed and the effective blue-light radiance were measured for different combinations
of base metal and welding wire. Three types of base metal were used: A1100P-H112,
Chapter VI
Blue-light Hazard from Gas Metal Arc Welding of Aluminum Alloys
118
A5083P-O and A6063BES-T5 (JIS, 2014). A1100P-H112 is essentially pure aluminum,
A5083P-O is an alloy containing 4%–5% magnesium, and A6063BES-T5 is an alloy
containing 0.45%–0.9% magnesium and additional elements other than magnesium. Three
types of welding wires were used: A1100WY, A4043WY and A5183WY (JIS, 2009).
A1100WY is essentially pure aluminum, A4043WY is an alloy containing small amounts
of magnesium and other non-magnesium elements, and A5183WY is an alloy containing
4%–5% magnesium (Table 1). Table 2 presents the combinations of base metals and welding
wires and their symbols used in this study. The welding currents were 100 A and 200 A.
Table 6.2 Combinations of base metal and welding wire tested and their symbols.
Symbol Base metal Important secondary
element Welding wire
Important
secondary element
P1W1 A1100P-H112 None A1100WY None
P5W5 A5083P-O Mg A5183WY Mg
P1W5 A1100P-H112 None A5183WY Mg
P5W1 A5083P-O Mg A1100WY None
P6W4 A6063BES-T5 Si A4043WY Si
6.3 Results
The effective blue-light radiance measured in this study was in the range of 2.9–20.0
W/cm2·sr. The maximum acceptable exposure duration per 10000 s corresponding to these
values was 5.0–34 s.
Figures 6.3(a) and 6.3(b) show typical examples of the spectral radiance of arcs for
GMAW-S and GMAW-P, respectively. Figure 6.4 shows the effective blue-light radiance
calculated from the spectral radiance for the two welding methods. The effective blue-light
radiance for GMAW-S was in the range 5.2–14.5 W/cm2·sr at welding current 150–250 A.
No data was obtained for GMAW-S at 100 A because of the instability of the welding. The
effective blue-light radiance for GMAW-P was in the range 5.7–20.0 W/cm2·sr at welding
Chapter VI
Blue-light Hazard from Gas Metal Arc Welding of Aluminum Alloys
119
current 100–250 A. The effective blue-light radiance was roughly proportional to the
welding current for both GMAW-S and GMAW-P. The effective blue-light radiance for
GMAW-P was 1.4 to 1.7 times greater than that for GMAW-S at each welding current.
(a) Spectral radiance of arc in GMAW-S with P5W5 (A5083P-O and A5183WY)
(b) Spectral radiance of arc in GMAW-P with P5W5 (A5083P-O and A5183WY)
Figure 6.3. Comparison of spectral radiance of arc for (a) GMAW-S and (b) GMAW-P.
Symbols Al and Mg indicate emission lines of aluminum and magnesium, respectively.
Chapter VI
Blue-light Hazard from Gas Metal Arc Welding of Aluminum Alloys
120
Figure 6.4. Effective blue-light radiance for GMAW-S and GMAW-P as a function of
welding current. Error bars represent the standard deviation calculated from five
measurements.
Figure 6.5 shows the spectral radiance for the following different combinations of base
metal and welding wire for GMAW-P: (a) P1W1, in which both base metal and welding
wire were pure aluminum; (b) P1W5, in which only the welding wire contained magnesium;
(c) P5W1, in which only the base metal contained magnesium; (d) P5W5, in which both
base metal and welding wire contained magnesium; (e) P6W4, in which both base metal
and welding wire contained silicon and small amounts of magnesium. Emission lines of
aluminum were observed in the spectral radiance for all the conditions tested, and intense
emission lines of magnesium were observed when the welding wire contained magnesium.
Figure 6.6 shows the effective blue-light radiance calculated from the measured
spectral radiance for the different combinations of base metal and welding wire. The
effective blue-light radiance at 200 A of the welding current was 2.1 to 2.7 times higher than
at 100 A for each combination. The effective blue-light radiance was different according to
Chapter VI
Blue-light Hazard from Gas Metal Arc Welding of Aluminum Alloys
121
the combination of base metal and welding wire. The effective blue-light radiance was the
highest for P5W5. The values for P1W5 were higher than those for P5W1. The lowest values
were observed for P6W4 and P1W1.
(a) Spectral radiance for P1W1 (b) Spectral radiance for P1W5
(c) Spectral radiance for P5W1 (d) Spectral radiance for P5W5
(e) Spectral radiance for P6W4
Figure 6.5. Spectral radiance of arc for different combinations of base metal and
welding wire in GMAW-P.
Chapter VI
Blue-light Hazard from Gas Metal Arc Welding of Aluminum Alloys
122
Figure 6.6. Effective blue-light radiance for different combinations. Error bars represent the
standard deviation calculated from five measurements.
6.4 Discussion
This study shows that the effective blue-light radiance that indicates the exposure level of
blue light to a welder in GMAW of aluminum alloys is in the range of 2.9–20.0 W/cm2·sr,
and that the corresponding maximum acceptable exposure duration per 10000 s is just 5.0–
34 s. This means that directly viewing the arc of GMAW of aluminum alloys is quite
hazardous. Thus, all welders and their helpers should wear eye protectors with a filter of the
appropriate shade number and look through it to protect themselves from blue light when
conducting arc welding.
In this study, the spectral radiance of the welding arc was measured in order to calculate
the effective radiance. These measured data, when combined with the spectral transmittance
of welding filters, can also be used to for the evaluation of the protection capability of
welding filters against blue light, which is of practical importance.
It is thought that some workers are often exposed to blue light when striking the arc,
because they mistakenly put on their face shields after starting the arc instead of
Chapter VI
Blue-light Hazard from Gas Metal Arc Welding of Aluminum Alloys
123
immediately before. If this brief exposure occurs many times in a few hours, the total
exposure times may easily exceed the maximum acceptable exposure duration estimated in
this study. Thus, every worker should always put on a face shield before starting the arc.
The brief exposure to blue light when striking the arc can be avoided by using auto-
darkening welding helmets, which have been increasingly used in workplaces. An auto-
darkening welding helmet has a filter that can change its transmittance and a sensor that
detects light from the arc. In an auto-darkening welding helmet, its filter turns dark when
the arc is being generated and transparent when the arc is off 25). Therefore, unlike a
conventional face shield, it is possible to wear an auto-darkening welding helmet at all times
regardless of the presence or absence of the arc.
This study also shows that the effective blue-light radiance increases with increasing
welding current when other conditions are the same (Figure 6.4 and Figure 6.6). This trend
was also observed previously for GMAW of mild steel using 100% CO2 as a shielding gas26).
Thus, the welding current is an important factor influencing the exposure level of blue light
emitted during the welding process. Welders should be particularly cautious about blue light
when conducting arc welding with high welding current.
As Figure 6.4 shows, the effective blue-light radiance is always higher for GMAW-P
of aluminum alloys than for GMAW-S of aluminum alloys when other conditions are the
same. This suggests that arc welding of aluminum alloys with pulsed current presents a
greater hazard than that with steady current. In recent years, the demand for arc welding of
thin plates of aluminum alloys has increased in order to produce lightweight equipment that
can be easily transported, and welding with pulsed current is widely used for this welding.
Workers need to recognize the very high hazard of the blue light when welding with pulsed
current.
For GMAW-P of aluminum alloys, the effective blue-light radiance is high for P1W5
Chapter VI
Blue-light Hazard from Gas Metal Arc Welding of Aluminum Alloys
124
and P5W5, in which the welding wire contains magnesium (Figure 6.6). This suggests that
magnesium contained in the wire enters the arc and emits intense blue light. In fact, the
spectral radiance for these cases (Figures 6.5(b) and 6.5(d)) shows that emission lines of
magnesium account for a large portion of the light emitted by the arc. This can be attributed
to the fact that, although the magnesium content of the welding wire is very low because
the boiling point of magnesium (1090°C) is considerably lower than that of aluminum
(2470°C), magnesium is preferentially vaporized from the welding wire and thus gives rise
to stronger emission. In particular, magnesium has strong emission lines at 450 nm and 470
nm in the very hazardous wavelength region (Figure 6.1). Consequently, it is concluded that
the hazard of the blue light emitted during GMAW-P of aluminum alloys is primarily
determined by the emission from magnesium contained in the welding wire.
In this study, the spectral radiance of the arc was measured at a distance of 2000 mm
using a spectroradiometer with a 48-mm-diameter aperture. This means that the light
emitted within the solid angle of 1.4 ° from the arc was measured. If the measurement had
been made at a different distance, light emitted within a different solid angle from the arc
would have been measured, and if the emission from the arc had been anisotropic, different
results would have been obtained. However, considering the mechanism of light emission
from a welding arc, the emission is essentially isotropic. Thus, the measurement distance is
expected to have a negligible effect on the present results.
6.5 Conclusions
It is very hazardous to view the arcs in gas metal arc welding of aluminum alloys. The
hazard is higher at higher welding currents, when pulsed welding currents are used instead
of steady welding currents, and when magnesium is included in the welding materials.
Welders and their helpers should use appropriate eye protectors in such arc-welding
Chapter VI
Blue-light Hazard from Gas Metal Arc Welding of Aluminum Alloys
125
operations. They should also avoid direct light exposure when starting an arc-welding
operation.
6.6 References
1) Sliney DH, Wolbarsht M, 1980. Safety with Lasers and Other Optical Sources, New
York, Plenum press.
2) Lyon TL, Marshall WJ, Sliney DH, Krial NP, Del Valle PF, 1976. Nonionizing radiation
protection special study No. 25-42-0053-77, Evaluation of the potential from actinic
ultraviolet radiation generated by electric welding and cutting arcs, Maryland, US Army
Environmental Hygiene Agency Aberdeen Proving Ground.
3) Okuno T, Ojima J, Saito, H, 2001. Ultraviolet radiation emitted by CO2 arc welding, The
Annals of Occupational Hygiene 45(7): 597–601.
4) Okuno T, Kohyama N, Serita F, 2005. Ultraviolet radiation from MIG welding of
aluminum, Safety & Health Digest 51(9): 2-5. (in Japanese)
5) Nakashima H, Utsunomiya A, Fujii N, Okuno T, 2014. Study of ultraviolet radiation
emitted by MIG welding of aluminum alloys, Journal of light metal welding 52(8): 290-
298. (in Japanese)
6) Nakashima H, Utsunomiya A, Fujii N, Okuno T, 2016. Hazard of ultraviolet radiation
emitted in gas tungsten arc welding of aluminum alloys, Industrial Health 54(2): 149–
159.
7) Nakashima H, Utsunomiya A, Takahashi J, Fujii N, Okuno T, 2016. Hazard of ultraviolet
radiation emitted in gas metal arc welding of mild steel, Journal of Occupational Health
58(5): 452-459.
8) The Japan Welding Engineering Society, 1980. Shakouhogogu no seinouhyouka tou ni
kansuru chousa kenkyu seika houkokusyo, A research report on the performance of eye
Chapter VI
Blue-light Hazard from Gas Metal Arc Welding of Aluminum Alloys
126
protectors against optical radiation, The Japan Welding Engineering Society. (in
Japanese)
9) Emmet EA, Buncher CR, Suskind RB, Rowe KW, 1981. Skin and eye diseases among
arc welders and those exposed to welding operations, Journal of Occupational Medicine
23: 85–90.
10) Würdemann HV, 1936. The formation of a hole in the macula: Light burn from
exposure to electric welding, American Journal of Ophthalmology 19(6): 457–460.
11) Minton J, 1949. Occupational diseases of the lens and retina, British Medical Journal
41: 392–394.
12) Naidoff MA, Slinkey DH, 1974. Retinal injury from a welding arc, American Journal
Ophthalmology 77(5): 663-666.
13) Romanchuk KG, Pollak V, Schneider RJ, 1978. Retinal burn from a welding arc,
Canadian Journal of Ophthalmology13: 120–122.
14) Uniat L, Olk RJ, Hanish SJ, 1986. Welding arc maculopathy, American journal of
ophthalmology 102: 394–395.
15) Cellini M, Profazio V, Fantaguzzi P, Barbaresi E, Longanesi L, Caramazza R, 1987.
Photic maculopathy by arc welding, A case report, International Ophthalmology 10:
157–159.
16) Brittain GPH, 1988. Retinal burns caused by exposure to MIG-welding arcs of two cases,
British journal of ophthalmology 72(8): 570-575.
17) Power WJ, Travers SP, Mooney DJ, 1991. Welding arc maculopathy and fluphenazine,
British journal of ophthalmology 75(7): 433–435.
18) Fich M, Dahl H, Fledelius H, Tinning S, 1993. Maculopathy caused by welding arcs, A
report of 3 cases, Acta ophthalmologica 71(3): 402-404.
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Blue-light Hazard from Gas Metal Arc Welding of Aluminum Alloys
127
19) Arend O, Aral H, Reim M, Wenzel M, 1996. Welders maculopathy despite using
protective lenses, Journal of Retinal and Vitreous Diseases 16(3): 257–259.
20) The American Conference of Governmental Industrial Hygienists, 2015. 2015
Threshold limit values for chemical substances and physical agents and biological
exposures indices, Cincinnati, American Conference of Governmental Industrial
Hygienists.
21) International Commission on Non-Ionizing Radiation Protection, 2013. ICNIRP
guidelines: On limits of exposure to incoherent visible and infrared radiation, Health
Physics 105(1): 74-96.
22) Marshall WJ, Sliney DH, Lyon TL, Krial NP, Del Valle PF, 1977. Evaluation of the
potential retinal hazards from optical radiation generated by electric welding and cutting
arcs. Aberdeen Proving Ground, MD: U.S. Army Environmental Hygiene Agency
Report, No. 42-0312-77.
23) Okuno T, 1986. Measurement of blue-light effective radiance of welding arcs, Industrial
Health 24(4): 213-226.
24) Peng CY, Lan CH, Juang YJ, Tsao TH, Dai YT, Liu HH, Chen CJ, 2007. Exposure
assessment of aluminum arc welding radiation, Health Physics 93(4): 298-306.
25) Comité Européen de Normalisation (CEN), 2009. Personal eye-protection. Automatic
welding filters. EN 379:2003+A1 2009, CEN.
26) Okuno T, Kobayashi N, 2013. Switching times of automatic darkening welding helmets,
Safety & Health 59(79): 2-6. (in Japanese).
Chapter VII
Summary and Conclusions
128
Chapter VII
Summary and Conclusions
7.1 Hazard of UVR
The Ultraviolet radiation (UVR) emitted during arc welding has been measured by
researchers and the related hazards have been quantitatively evaluated1-7), according to the
acceptance criteria of The American Conference of Governmental Industrial Hygienists
(ACGIH) and International Commission on Non-Ionizing Radiation Protection (ICNIRP)8,9).
In these studies, the effective irradiance of UVR emitted during gas tungsten arc welding
(GTAW) and gas metal arc welding (GMAW) of aluminum alloys and GMAW of mild steel
was measured. Dependence of effective irradiance on the welding current and adaptation of
the inverse square law of distance were also verified. In arc welding, welding results, such
as the shape of weld bead and the depth of fusion, have been dependent on welding materials
(components of a base metal and a filler metal), the pulsed current, the shielding gas, and
the type of electrodes. It is considered that these elements also have an effect on UVR,
because there is a close relationship between the state of the arc and the welding result.
However, the influence of these elements on the hazard from UVR has not yet been
investigated. In addition, because the UVR emitted during arc welding is influenced by
reflections from the surface of a base metal and the liquid surface of molten pool, and by
absorption/scattering due to fumes, the effective irradiance of UVR is thought to be
subjected to the angular dependence. However, it is considered to be insufficient because
the angular dependency of the effective irradiance had only been investigated regarding the
angle from the surface of the base material in GMAW of mild steel5).
In actual welding workplaces, the arc welding is performed under various conditions;
hence, welding workers and surrounding workers are exposed to various environments.
Chapter VII
Summary and Conclusions
129
Therefore, it is necessary to clarify the influence of elements: pulsed current, shielding gas,
type of electrodes and angular dependence, as a basis to improve the welding ambient
environment.
7.1.1 Hazard level of UVR in this study
In this study, the effective irradiance of UVR observed at 500 mm from the arcs was 0.09–
13 mW/cm2. The allowable daily exposure time calculated from these irradiances was 0.23–
33 s. Therefore, because the cumulative allowable exposure time calculated by the effective
irradiance is extremely short, it is considered that the cumulative exposure time of welding
workers easily exceeds the threshold value when exposed to a welding arc without applying
appropriate precautionary measures. Table 7.1 shows the effective irradiance and the
allowable exposure time for each type of welding for various materials.
Table 7.1 Effective irradiance and allowable exposure time for each welding
Type of
welding Base metal
welding
current (A)
Effective irradiance
(mW/cm2)
Allowable
exposure time (s)
GMAW
Aluminum 100-250 0.33-10 0.30-9.1
Mild steel 100-350 0.51-13 0.23-5.9
Magnesium 100-175 4.6-7.8 0.39-0.65
GTAW Aluminum 100-200 0.10-0.91 3.3-33
Magnesium 100-200 0.85-8.9 0.30-3.5
Assuming that the daily working time is 8 hours and that the effective irradiance of
UVR decreases relative to the inverse square law of distance, the allowable exposure time
on the fixed exposed surface at each distance is shown in Table 7.2. In an actual workplace,
arcs rarely occur continuously for 8 hours, and because workers are moving, it is not
considered that only certain surfaces will be exposed to UVR. Therefore, the actual
Chapter VII
Summary and Conclusions
130
allowable exposure time is underestimated. However, even at a distance of 5 m from the arc,
exposure to UVR is hazardous irrespective of the UVR intensity, thus it is believed that
prolonged exposure is also hazardous. In cases where arc welding is performed, it is
necessary to take precautions to ensure that all surrounding workers are not exposed to the
UVR emitted by the arc.
Table 7.2 Relationship between the allowable exposure time and the distance from the arc
Distance (m) 0.5 1 5 10 20
Allowable exposure time(s) 0.23-
33
0.92-
130
23-
3300
92-
13000
368-
52000
7.1.2 Factors affecting hazard level of UVR
In this study, it was revealed that five new factors, besides welding current, influence the
hazard level of UVR. These elements exhibit the following characteristics. In addition to
workers engaged in arc welding, workers engaged in other tasks around arc welding must
be fully aware of these factors in order to protect themselves from exposure to UVR.
(a) Welding current
Consistent with previous studies, the influence of welding current on the hazard level of
UVR was confirmed1-7). The effective irradiance of UVR emitted during GTAW (Figure
2.4) and GMAW (Figure 3.4) of aluminum alloys, during GMAW of mild steel (Figures 4.2
and 4.3) and during GTAW and GMAW of magnesium alloys (Figure 5.2) sharply increases
with the increase of welding current, as measured in this study. Welding current is, therefore,
an important factor affecting the hazard level of UVR emitted during arc welding.
(b) Elements contained in welding materials
Chapter VII
Summary and Conclusions
131
In this study, the hazard level of UVR was strongly influenced by the elements contained in
base metals and filler metals, as shown by the measured effective irradiance of UVR emitted
during GTAW and GMAW of aluminum alloys (Figures 2.4 and 3.4). In particular, the
hazard level of UVR emitted during GMAW was more strongly influenced by magnesium
in the welding wire than by magnesium in the base metal.
Aluminum alloys containing magnesium are currently widely used because they have
excellent strength characteristics after welding. Welding operators and their supervisors
should be aware that UVR with high hazardous level is emitted during arc welding of
aluminum alloys containing magnesium.
(c) Pulsed current
It was clarified that the hazard level of UVR is strongly affected by the pulsed current, as
shown by the measured effective irradiance of UVR emitted during GMAW of aluminum
alloys and mild steel (Figures 3.7 and 4.3). In addition, the hazard level becomes higher
particularly in the low current range as compared to the steady current. In recent years, the
demand for welding structures corresponding to the environment has increased, and welding
of thin plates with a thickness of 3 mm or less is increasing. Because the pulsed current
provides arc stability in the low current range, it is anticipated that the use of pulsed current
will increase in the future. Therefore, workers in the vicinity of arc welding have to be aware
that the hazard level of UVR is high even in the low current range when using pulsed current.
(d) Shielding gas
In this study, it was revealed that the type of shielding gas used during GMAW influences
the hazard level of UVR. In GMAW of mild steel, as shown in Fig. 4.2, the shielding gas
affected the effective irradiance at welding current of 300 A or more, and the effective
Chapter VII
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132
irradiance was almost doubled in 80% Ar + 20% He compared to 100% CO2. In the case of
magnesium alloy GTAW, as shown in Figure 5.3, the effective irradiance approximately
doubled in 50% Ar + 50% He compared to 100% Ar. In contrast, in GMAW, due to added
He, the amount of fumes generated during arc welding increased and the effective
irradiation decreased.
In recent years, the use of 80% Ar + 20% He has been increased in GMAW of mild
steel, due to less spatter generation and easiness of post-weld treatment. Therefore, it is
considered that special attention is required for exposure to UVR.
(e) Type of electrode
The effective irradiance of UVR emitted during GTAW of aluminum alloys and magnesium
alloys is affected by the type of electrode. As shown in Figure 2.8 and Figure 5.3, the
effective irradiance is about 10-20% higher when using electrodes containing oxides than
when using pure tungsten electrodes.
Generally, electrodes containing oxides are more durable, so continuous welding is
possible for a longer period of time than with pure tungsten electrodes. Therefore, when an
electrode containing an oxide is used, it is considered that the cumulative exposure time of
UVR per day becomes longer. Welding workers employees should be aware that the hazard
level of UVR is high, in recent years, as using of oxide-containing electrodes is increasing
due to high working efficiency.
(f) Angle from welding arc
The hazard level of UVR depends on the angle from a welding arc, according to the effective
irradiance of GTAW and GMAW of aluminum alloys measured in this our study (Figures
2.6 and 3.5). Regardless of the welding method, in flat-position welding, the effective
Chapter VII
Summary and Conclusions
133
irradiance of UVR depends on the angle from the surface of the base metal. The angle with
the highest effective irradiance of UVR is 40°–50°. Therefore, when welding workers
employees perform arc welding in a normal posture, the hazard level of UVR is highest
around their head and neck.
7.2 Hazard level of blue light in this study
Arc welding also emits intense visible light. An extremely large number of workers is
predicted to be exposed to visible light by accidentally or mistakenly looking directly at the
welding arc without adequate protection. It has been reported that many light-induced
retinal injuries have occurred in people who were looking at welding arcs without adequate
protection10-19). The light-induced retinal injury with arc welding is a severe disorder that
has a significant impact on daily life. However, measurement of the blue light during arc
welding has not been actively studied. In particular, few studies have measured the blue
light emitted during arc welding of aluminum alloys20-22), and no reliable data on blue-light
effective radiance have been reported. In this study, similar to the measurement of the
effective irradiance of UVR, the effective radiance of blue light emitted during GMAW of
aluminum alloys was experimentally measured under welding conditions simulating an
actual welding operation. In addition, the effective blue light radiance of the welding arc
was measured under a stable environment with a fixed welding arc.
In this study, the radiance distributions in visible radiation emitted during GMAW of
aluminum alloys under various conditions were measured, and the hazard of blue light was
quantitatively evaluated according to the recommendation of the ACGIH23). The effective
radiance of blue light measured in this study was in the range of 2.9–20.0 W/cm2·sr. The
corresponding maximum acceptable exposure duration per day when the exposure time is
shorter than 10000 s was only 5.0–34 s. Therefore, as the cumulative acceptable exposure
Chapter VII
Summary and Conclusions
134
duration per day is very short, it is considered that directly looking at welding arcs during
GMAW of aluminum alloys, without appropriate prevention measures, will exceed the
threshold exposure duration. The effective radiance of blue light emitted during GMAW of
aluminum alloys was higher at a higher welding current than at a lower welding current.
This trend is similar to the effective radiation of blue light when welding mild steel. The
welding current was also an important factor affecting the hazard level of blue light emitted
during welding. In addition, the effective radiance of blue light increased when the pulsed
current was used and when the welding materials contained magnesium.
7.3 Measures against light emitted during arc welding
The effective irradiance of UVR measured at 500 mm from the welding arc was 0.09–12.9
mW/cm2 in this study. According to these irradiance values, the allowable maximum
exposure time per day was just 0.23–33 s. Furthermore, the effective radiance of blue light
measured in this study was 2.9–20.0 W/(cm2·sr). The maximum acceptable exposure
duration corresponding to these radiance values per 10000 s was 5.0–34 s. Because UVR
and blue light with high hazard levels are emitted during arc welding, it is hazardous to
directly expose workers to these light sources without adequate protection. Therefore, it is
considered that protective measures are necessary. Here, two cases were considered: (1)
Protection measures of welding workers. (2) Protection measures of surrounding workers
engaged in tasks other than welding. Regarding UVR, protection measures are necessary
for the eyes and the skin, because keratoconjunctivitis and erythema have been reported in
actual welding places24,25). Regarding blue light, eye protection measures are required,
because retinal injury is caused by staring looking at a welding arc10-19). Furthermore,
because UVR and blue light are simultaneously emitted during arc welding, all protection
measures should be taken at the same time.
Chapter VII
Summary and Conclusions
135
7.3.1 Welding workers
As a protective measure against keratoconjunctivitis caused by UVR and retinal injuries
caused by blue light, it is essential to look at the welding arc through a filter with an
appropriate light shielding number standardized by the JIS26), etc. Welding workers have
been using a face shield with appropriate filters. However, eye injuries due to arc welding
have been reported by welding workers despite wearing a face shield. Because the filter
attached to a face shield is very dark, the welding spot is not obvious before the arc is struck.
Therefore, some welding workers wear the face shield immediately just before the arc is
struck, therefore they may be exposed to UVR and blue light by accidentally wearing a face
shield without a filter after the arc is generated. Although the accidental exposure is brief
for each strike of the arc, exposure may occur recurrently, because workers usually strike
an arc repeatedly during a day. Consequently, another hazard is that total exposure time
could easily exceed the allowable daily exposure time determined in this study.
The brief exposure to UVR and blue light when striking the arc can be avoided by
using auto-darkening welding helmets, which have been increasingly used in workplaces.
An auto-darkening welding helmet has a filter that changes its transmittance and a sensor
that detects light from the arc. In an auto-darkening welding helmet, the filter turns dark
when the arc is being generated and transparent when the arc is off 27,28). Therefore, instead
of a conventional face shield, it is possible to wear an auto-darkening welding helmet at all
times regardless of the presence of the arc.
It is necessary for welding workers to wear appropriate welding protective equipment
to prevent their skin from UVR exposure. As clarified in Chapters 2 and 3, the effective
irradiance of UVR depends on the angle from the base material and becomes strongest near
the welding worker's head and neck. Welding workers must completely protect these areas
with a face shield or other protective gear. In particular, during hot summer weather, the risk
Chapter VII
Summary and Conclusions
136
of exposure to UVR is higher, because welding workers often neglect to wear neck
protection.
7.3.2 Surrounding workers engaged in tasks other than welding.
Table 7.2 shows the relationship between allowable daily exposure time and the distance
from arcs calculated by the inverse square law of distance. For example, the range of
allowable permitted daily exposure time of UVR is 23–3300 s at a distance of 5 m from the
welding arc. Thus, even at a distance of 5 m from the arc, exposure to UVR is hazardous
when the emitted UVR is intense. Furthermore, prolonged exposure is dangerous even when
the emitted UVR is weak. Thus, in workplaces where arc welding is performed, it is
necessary to take precautions to ensure that surrounding workers are not exposed to the
UVR emitted by welding arcs.
The workplaces located near the arc welding area need to be compartmentalized in
order to protect the eyes and the skin of the workers who perform tasks other than arc
welding in the surrounding areas (Article 325 of the Occupational Health and Safety
Regulations stipulates that companies must partition places where a hazard of diverging
intense light, such as a welding arc, exists). However, when partitioning by walls and opaque
materials, the work space becomes separated and workers might possibly feel a sense of
pressure or loneliness.
Therefore, as a reference experiment in this study, the spectral irradiance was
measured through a glass plate (colorless), a polycarbonate plate (colorless) and a light-
shielding curtain (yellow or green) during 100% CO2 welding of mild steel. The
experimental arrangement was the same as that shown in Figure 3.2, and the welding current
was 100 A. Figure 7.1 shows the measurement results. Among the hazardous lights emitted
by arc welding to the surrounding environment, UVR can be blocked by installing a glass
Chapter VII
Summary and Conclusions
137
plate or a polycarbonate plate, or another suitable material. In addition, it is possible to
reduce the hazard from blue light with a yellow light-shielding curtain for welding. The
transmittance through the green light-shielding curtain was too low to measure the spectral
irradiance. Therefore, it is thought that a yellow light-shielding curtain is the most suitable
partitioning material to protect from UVR emitted to the surrounding environment. However,
the supervisor needs to educate the surrounding workers to not directly look at the welding
arc, because this curtain is insufficient to protect from blue light.
Figure 7.1 The spectral distribution of the welding arc that passed through each light
shielding material.
7.4 Application of the results of this research
As mentioned above, the hazard levels of UVR and blue light of the welding arcs emitted
under various welding conditions are high and adequate protection measures against these
lights are necessary. Eye protectors, face shields, work clothes and light shielding curtains
for welding are commonly used as protective equipment against welding arcs. Only the filter
Chapter VII
Summary and Conclusions
138
lens attached to the eye protector and the filter plate attached to the face shield, whose light
shielding performance value is specified by JIS26), are shown in Figure 7.2. There is no
regulation regarding the light shielding performance of other light shielding protective
equipment, and unified performance evaluation has not been performed yet. In addition, JIS
has defined the light blocking effect values of the filter lens and filter plate against UVR
and visible light. Transmittance at 313 nm and 365 nm for ultraviolet radiation and average
transmittance for visible light have been determined. However, it is difficult to
quantitatively evaluate the performance of light shielding protectors by these values only,
because the hazard levels of UVR and blue light vary depending on the wavelength.
Additionally, the intensity distribution of light emitted during arc welding is influenced by
the base metal and filler metal.
The quantitative evaluation of performance is considered necessary for the selection
of light shielding protective equipment in the actual work site. Quantitative evaluation of
the performance of light shielding protective equipment becomes possible by applying the
spectral irradiance, the effective irradiance and the spectral radiance measured in this study,
provided that it is possible to measure the spectral transmittance of a light shielding protector.
The effective irradiance of UVR transmitted through the light shielding protector can
be obtained by the following equation, and evaluation of protector performance is possible.
𝐸𝑒𝑓𝑓′ = ∑ 𝐸𝜆・
400
180
𝑆(𝜆)・𝑇(𝜆)・∆𝜆 ・・・・・(1)
In this equation, Eeff’ is the effective irradiance after transmission (W/cm2), Eλ is the spectral
irradiance at wavelength λ (W/(cm2·nm)), S(λ) is the relative spectral effectiveness at
wavelength λ, T(λ) is the spectral transmittance at wavelength λ, and Δλ is the wavelength
Chapter VII
Summary and Conclusions
139
bandwidth (nm).
The maximum exposure time: tmax’(s) per day against the effective irradiance when
the protected skin or eye is irradiated with UVR is obtained using Equation (2):
tmax′ =
3
Eeff′. ・・・・・(2)
In addition, the effective radiance of blue light transmitted through the light shielding
protector can be obtained by the following equation, and evaluation of a protector
performance is possible.
LB′ = ∑ Lλ ·
700
305
B(λ) · T(λ) · ∆λ, ・・・・・(3)
LB’ is the effective radiance (W/(cm2·sr )), LA is the spectral radiance W/(cm2·sr·nm) of the
wavelength λ, T(λ) is the spectral transmittance at wavelength λ, and B(λ) is the blue-light
hazard function.
The maximum acceptable exposure duration after transmittance through work clothing
in one day, t’max (s), based on the effective blue-light radiance can be obtained with Equation
(4):
t′max =100
LB. ・・・・・(4)
Chapter VII
Summary and Conclusions
140
Personal eye protectors for optical radiations Personal face protectors for welding
Figure 7.2 Protective equipment for welding in general using
7.4.1 Adaptation example of quantitative evaluation on UVR shielding performance
for work clothes
Workers working around arc welding work including welding workers usually wear work
clothes. Working clothes protect from exposure to UVR, but the effectiveness against UVR
emitted during arc welding has not been quantitatively evaluated. Therefore, quantitative
evaluation of light shielding performance of work clothes was attempted with equations (1)
and (2). Work clothes subjected to the experiment are similar to widely used by workers;
clothes with a composition of 65% polyethylene + 35% cotton (130 g/m2) or 100% cotton
(180 g/m2) are generally used in the summer, and with 100% cotton (280 g/m2) or 100%
aramid are used in the winter. Details of the fabric are shown in Table 7.3.
The spectral transmittance of each fabric was experimentally obtained using a
spectrophotometer (Figure 7.3). In addition, the spectral irradiance and effective irradiance
of UVR emitted during GMAW-P of aluminum alloy measured in this study were applied,
and the effective irradiance and allowable exposure time after transmittance through each
fabric were calculated. The welding current used is 250 A. Table 7.3 shows the effective
irradiance after transmittance through each fabric and the allowable exposure time for each
distance.
Filter lens
Filter plate
Chapter VII
Summary and Conclusions
141
As described above, provided that the spectral transmittance of the light shielding
protector can be obtained, quantitative evaluation of light shielding performance against
UVR of various protectors becomes possible by adapting the data obtained in this study.
Figure 7.3 Spectral transmittance of each type of clothes
Table 7.3 Shielding performance of working clothes against UVR
Type of fabric ― PE+CO* Cotton (100%) Aramid**
Weight (g/m2) ― 130 180 280 210
Effective irradiance (mW/cm2) 10 0.66 0.08 0.00 0.00
Average transmittance (%) 100 6.9 1.0 0.03 0.09
Allowable exposure time (s) (50 cm) 0.3 4.5 35 ∞ ∞
Allowable exposure time (s) (5 m) 30 450 3500 ∞ ∞
Allowable exposure time (s) (10 m) 120 1800 14000 ∞ ∞
* PE+CO: 65% polyester + 35% cotton,
**Aramid: DuPont™ Nomex®
Chapter VII
Summary and Conclusions
142
7.4.2 Adaptation example of quantitative evaluation of light shielding performance
against blue light for filter lens and filter plates
JIS specifies the average transmittance in the visible radiation range with respect to the light
shielding performance against the blue light of the filter lens and filter plate as shown in
Figure 7.4. However, as clarified in this research, in arc welding, the spectral distribution of
the welding arc is different due to the influence of the welding material. Therefore, the
performance evaluation of the light shielding protector according to the current JIS standard
is insufficient, and it is considered that performance evaluation is required when considering
the hazard level of each wavelength.
The light shielding performance of filter lens and filter plates were quantitative evaluated
with equations (3) and (4). Figure 7.5 and Figure 7.6 show the experimentally determined
spectral transmittance of the filter lens and filter plate. For the spectral radiance, the value
measured in GMAW-P of the aluminum alloy measured in this study was applied. The
welding current used was 250 A. The effective radiance after transmittance through the filter
lens or filter plates and the allowable exposure time are shown in Table 7.4 and Table 7.5.
As described above, after the spectral transmittance of the filter lens and the filter plate is
obtained, it is possible, by applying the data measured in this study, to quantitatively
evaluate the light shielding performance against the blue light corresponding to various
welding conditions.
Chapter VII
Summary and Conclusions
143
#1.4 #1.7 #2 #3
Filter lens
#9 #10 #11 #12
Filter plate
Figure 7.4 Filter lens and plate for personal eye protectors for optical radiations
Figure 7.5 Spectral transmittance of filter lens for visible radiation wavelengths
Chapter VII
Summary and Conclusions
144
Figure 7.6 Spectral transmittance of filter plates for visible radiation wavelengths
Table 7.4 Shielding performance of filter lens against blue light
Shade number. ― #1.4 #1.7 #2 #3
Effective radiance (W/(cm2·sr)) 20 2.7 1.6 0.54 0.25
Allowable exposure duration (s) 5.0 37 64 180 390
Table 7.5 Shielding performance of filter plates against blue light
Shade number. ― #9 #10 #11 12
Effective radiance (W/(cm2·sr)) 20 4.2×10-4 2.2×10-4 7.3×10-5 1.9×10-5
Allowable exposure duration (s) 5.0 ∞ ∞ ∞ ∞
7.5 General conclusion
It became clear that the welding arcs measured in this study include high levels of hazardous
radiation of UVR and blue light. It is suggested that sufficient protection measures are
necessary, because the exposure to welding arcs for welding and surrounding employees is
at a high hazard level.
Chapter VII
Summary and Conclusions
145
The main factors affecting the hazard level of UVR and blue light are the following.
(1) Welding current: The hazard level of UVR and blue light increases with increasing
welding current.
(2) Elements contained in welding materials: The hazard level of UVR and blue-light were
affected by welding wire containing magnesium, in particular.
(3) Pulsed current: The hazard level of UVR and blue light increases by using pulsed current.
In particular, the hazard level increases in the low current range.
(4) Shielding gas: The shielding gas influences the metal transfer mode and the depth of
fusion, and as a result influences the hazard level of UVR.
(5) Type of electrode: The effective irradiance of UVR is about 10-20% higher when using
electrodes containing oxides than when using pure tungsten electrodes.
(6) Angle from welding arc: In flat-position welding, the hazard level of UVR around the
head and neck of the welding worker is higher.
In addition, the following protection measures are considered effective for hazardous
light.
(1) Welding workers must constantly wear suitable welding protective equipment prescribed
by JIS. as protection measures against UVR and blue light. In particular, auto-darkening
welding helmets are effective against UVR and blue light exposure.
(2) The surrounding workers during a welding operation, need protection measures against
UVR, and it is effective to compartmentalize the welding space using welding curtains as a
protection measure. In addition, safety education related to photoretinopathy of workers is
necessary to protect from blue light exposure.
(3) It is desirable to use constant current as the welding current rather than pulsed current.
Chapter VII
Summary and Conclusions
146
(4) It is necessary that better care should be taken against UVR and blue light exposure,
when magnesium is included in the welding material.
The following conclusions were obtained in each chapter.
In Chapter II, the hazard of UVR emitted during GTAW of aluminum alloys was
quantitatively evaluated. The following conclusions were obtained.
GTAW of aluminum alloys leads to the emission of intense UVR. Exposure to this
radiation is considered hazardous according to the ACGIH guidelines. UVR exhibits the
following hazardous characteristics. (1) It is more hazardous at higher welding currents. (2)
It is more hazardous when the welding materials include magnesium. (3) It is more
hazardous for melt-run welding. (4) The hazard level depends on the direction of emission
from the arc. (5) Electrodes containing oxides yield a stronger hazard than electrodes of
pure tungsten. (6) Under the welding conditions typically used at actual workplaces, the
hazard of GTAW is approximately 1/10 of that of GMAW.
In Chapter III, the hazard of UVR emitted during GMAW of aluminum alloys was
quantitatively evaluated and the following conclusions were obtained.
GMAW of aluminum alloys leads to the emission of intense UVR. Exposure to this
radiation is considered hazardous according to ACGIH guidelines. UVR exhibits the
following hazardous characteristics. (1) It is more hazardous at higher welding currents. (2)
It is more hazardous when the welding materials include magnesium. In particular, the
hazard level of UVR becomes higher when the welding wire contains magnesium. (3) The
hazard level depends on the direction of emission from the arc. (4) It is more hazardous
when using pulsed welding currents than using steady welding currents.
Chapter VII
Summary and Conclusions
147
In Chapter IV, the hazard of UVR emitted during GMAW of mild steel was quantitatively
evaluated. The following conclusions were obtained.
GMAW of mild steel leads to the emission of intense UVR. The exposure to this
radiation is considered hazardous according to the ACGIH guidelines. This UVR hazard
exhibits the following characteristics. (1) It is more hazardous at higher welding currents
than at lower welding currents. (2) At higher welding currents, it is more hazardous in 80%
Ar + 20% CO2 shielding gas than in 100% CO2. (3) It is more hazardous when using pulsed
welding currents than using non-pulsed welding currents. (4) It appears to depend on the
metal transfer, because the hazard of the UVR emitted during spray transfer is the highest.
In Chapter V, the hazard of UVR emitted during GMAW and GTAW of magnesium alloys
was quantitatively evaluated and the following conclusions were obtained.
The GTAW and GMAW-P of magnesium alloys leads to the emission of intense UVR.
According to the ACGIH guidelines, exposure to this radiation is considered to be hazardous.
This UVR hazard exhibits the following characteristics. (1) The hazard of UVR generated
during welding is higher for GMAW-P (pulsed current) than for GTAW. (2) The hazard of
UVR is higher at higher welding currents. In addition, GTAW is more susceptible to the
welding current than GMAW-P. (3) The hazard of UVR emitted during GTAW increases
when the shielding gas contains helium. (4) The hazard of UVR during GTAW is increased
with the use of cerium oxide tungsten electrodes. (5) The UVR in GMAW-P is strongly
affected by fumes generated during welding, and the level of hazard level is reduced with
the increase of the amount of fumes.
In Chapter VI, the blue-light hazard from GMAW of aluminum alloys was quantitatively
evaluated and the following conclusions were obtained.
It is highly hazardous to look directly at the arcs in gas metal arc welding of aluminum
Chapter VII
Summary and Conclusions
148
alloys. (1) The hazard is higher at higher welding currents. (2) The hazard is higher when
using pulsed welding currents compared to steady welding currents. (3) The hazard is higher
when magnesium is included in the welding materials. Welding workers and their assistants
should use appropriate eye protectors in arc welding operations. They should also avoid
direct light exposure when starting an arc welding operation.
7.6 References
1) Lyon TL, Marshall WJ, Sliney DH, Krial NP, Del Valle PF, 1976. Nonionizing radiation
protection special study No. 42-0053-77, Evaluation of the potential from actinic
ultraviolet radiation generated by electric welding and cutting arcs. US Army
Environmental Hygiene Agency Aberdeen Proving Ground ADA033768, Maryland.
2) Sliney D, Wolbarsht M, 1980. Safety with Lasers and Other Optical Sources. Plenum
Press. New York.
3) Okuno T, 1986. Measurement of blue-light effective radiance of welding arcs. Industrial
Health 24(4): 213-226.
4) Okuno T, 1987. Measurement of ultraviolet radiation from welding arcs, Industrial
Health 25: 147-156.
5) Okuno T, Ojima J, Saito H, 2001. Ultraviolet radiation emitted by CO2 arc welding. The
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aluminum arc welding radiation, Health Physics 93(4): 298-306.
7) Okuno T, Saito H, Hojo M, Kohyama N, 2005. Hazard evaluation of ultraviolet radiation
emitted by arc welding and other processes, Occupational Health Journal 28(6): 65-71.
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Summary and Conclusions
149
8) The American Conference of Governmental Industrial Hygienists, 2015. 2015 TLVs®
and BEIs®. American Conference of Governmental Industrial Hygienists. Cincinnati.
9) International Commission on Non-Ionizing Radiation Protection, 2004. ICNIRP
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and 400 nm (incoherent optical radiation), Health Physics 87(2): 171-186.
10) Uniat L, Olk RJ, Hanish SJ, 1986. Welding arc maculopathy, American Journal of
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11) Cellini M, Profazio V, Fantaguzzi P, Barbaresi E, Longanesi L, Caramazza R, 1987.
Photic maculopathy by arc welding. A case report, International ophthalmology 10:
157–159.
12) Brittain GPH, 1988. Retinal burns caused by exposure to MIG-welding arcs: report of
two cases, The British journal of ophthalmology 72: 570–575.
13) Power WJ, Travers SP, Mooney DJ, 1991. Welding arc maculopathy and fluphenazine,
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14) Fich M, Dahl H, Fledelius H, Tinning S, 1993. Maculopathy caused by welding arcs: A
report of 3 cases, Acta ophthalmologica 71: 402–404.
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protective lenses, The Journal of Retinal and Vitreous Diseases 16: 257–259.
16) Würdemann HV, 1936. The formation of a hole in the macula. Light burn from exposure
to electric welding, American journal of ophthalmology 19: 457–460.
17) Minton J, 1949. Occupational diseases of the lens and retina, British medical journal 41:
392–394.
18) Naidoff, MA, Slinkey DH, 1974. Retinal injury from a welding arc, American journal
of ophthalmology 77(5): 663-666.
Chapter VII
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19) Romanchuk KG, Pollak V, Schneider RJ, 1978. Retinal burn from a welding arc,
Canadian journal of ophthalmology 13: 120–122.
20) Peng C, Lan C, Juang Y, Tsao T, Dai Y, Liu H, Chen C, 2007. Exposure assessment of
aluminum arc welding radiation, Health Physics 93(4): 298-306.
21) Marshall WJ, Sliney DH, Lyon TL, Krial NP, Del Valle PF,1977. Evaluation of the
potential retinal hazards from optical radiations generated by electric welding and
cutting arcs, Aberdeen proving ground, MD. U.S. Army Environmental Hygiene
Agency Report No. 42-0312-77.
22) Okuno T, 1986. Measurement of blue-light effective radiance of welding arcs, Industrial
Health 24: 213-226.
23) The American Conference of Governmental Industrial Hygienists, 2016. 2016 TLVs and
BELs with 7th edition documentation CD-ROM, optical radiation: light and near-
infrared radiation, ACGIH: 144-152.
24) The Japan Welding Engineering Society, 1980. Shakouhogogu no seinouhyouka tou ni
kansuru chousa kenkyu seika houkokusyo [A research report on the performance of eye
protectors against optical radiations], The Japan Welding Engineering Society, Japan,
Tokyo. (in Japanese)
25) Emmet EA, Buncher CR, Suskind RB, Rowe KW, 1981. Skin and eye diseases among
arc welders and those exposed to welding operations, Journal of Occupational Medicine
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26) Japan Standards Association, Japan Safety Appliances Association, 2003. Personal eye
protectors for optical radiations, JIS T8141, Japan Safety Appliances Association.
27) Comité Européen de Normalisation (CEN), 2009. Personal eye-protection. Automatic
welding filters. EN 379:2003+A1:2009, CEN.
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28) Okuno, T.; Kobayashi N, 2013. Switching times of automatic darkening welding
helmets. Safety & Health 59(79): 2-6. (in Japanese)
152
Acknowledgments
This paper was written under the guidance of Professor Shunitz Tanaka. First and foremost,
my sincere thanks to Professor Shunitz TANAKA for his polite guidance, encouragement
and advice during this Ph.D. project.
I would like to sincere thank Associate Professor Masaaki KURASAKI, I have been given
a lot of his teaching and advice during writing this paper.
I offer my sincerest gratitude Prof. Tsutomu OKUNO, Tokyo Metropolitan University, an
Optical radiation expert, for his advice and encouragement during this Ph.D. project. In
particular, he has taught me knowledge and experimental method on optical radiation.
I must express my gratitude to Professor Yuichi KAMIYA and Professor Takashi SAITO
who reviewed this paper and gave me valuable teaching and advice.
I would like to thank my supervisor Prof. Nobuyuki FUJII, Polytechnic University, has
offered much advice and insight throughout my Ph.D. project. In addition, he taught me the
attitude, thought and humanity as a researcher.
I would like to thank Yoshihisa Ishiba, Institute director, Ymamamoto Kogaku Co., Ltd, I
have been given a valuable opportunity to experiment with spectral transmittance of
protective equipment.
I would like to thank my dear juniors, Akihiro UTSUNOMIYA and Junya TAKAHASHI,
they have always helped me through public and private. Thanks also go to my colleagues
and friends in Polytechnic University for their help in many ways.
I am very grateful for the students and graduates of Fujii Laboratory, their experimental aid
always helped me.
Finally, I want to thank to my family. In particular, my mother, Mieko NAKASHIMA, my
father, Takeomi NAKASHIMA, and my beloved children, Yoshihiro NAKASHIMA, Yuto
NAKASHIMA and Nozomu NAKASHIMA, are always proud and encouraging. Most
importantly, I must thank my wife, Machiko NAKASHIMA, for her unconditional love and
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support. Without their encouragement and support, it was impossible to complete this Ph.D.
project.